r 


THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

RIVERSIDE 


THE    SCIENTIFIC   STUDY 
OF   SCENERY 


J-LO/OA57 

THE 

SCIENTIFIC   STUDY 

*~*~ ' 

OF    SCENERY 


BY 

JOHN    E?  MARK,   M.A.,   F.R.S. 

FELLOW   OF   ST.   JOHN'S   COLLEGE,    CAMBRIDGE 


WITH    TWENTY-ONE    ILLUSTRATIONS 
AND   NUMEROUS   DIAGRAMS   IN   THE  TEXT 


NEW  YORK :    NEW  AMSTERDAM  BOOK  CO. 

LONDON  :    METHUEN  &  CO. 

1900 


PREFACE 

MANY  books,  as  Sir  A.  Geikie's  Scenery  of 
Scotland  and  Sir  J.  Lubbock's  Scenery  of 
Switzerland,  give  an  account  of  the  origin  of  the 
scenery  of  limited  areas,  but  I  believe  that  there 
is  room  for  an  English  work  which  treats  of  the 
origin  of  scenery  in  general. 

Under  the  title  The  Scientific  Study  of  Scenery 
I  have  written  a  work  which  may  be  regarded  as  an 
Introductory  Treatise  on  Geomorphology,  a  subject 
which  has  sprung  from  the  union  of  Geology  and 
Geography. 

I  have  tried  to  make  the  work  useful  to  the 
student,  and  also  to  rouse  the  interest  of  the  general 
reader,  and  hope  that  I  have  not  thereby  rendered 
it  unpalatable  to  both. 

For  those  who  desire  to  pursue  the  study  of  the 
subject,  I  have  introduced  numerous  references  to 
works  of  a  more  technical  character.  In  addition 
to  those  cited  in  the  text,  I  would  refer  the  student 
to  Professor  J.  Geikie's  Earth  Sculpture  and  Professor 
W.  M.  Davis's  Physical  Geography.  These  books 
have  appeared  since  the  text  was  written. 

To  Mr.  Geo.  Allen,  of  Ruskin   House,  I  am  in- 


vi  PREFACE 

debted  for  permission  to  make  the  quotations  from 
Mr.  Ruskin's  works,  and  also  for  the  use  of  the 
block  from  which  Figure  3  is  printed  ;  I  wish  to 
thank  Mr.  W.  G.  Collingwood  for  leave  to  use  this 
figure.  My  thanks  are  due  to  the  Hon.  D.  W. 
Carnegie  and  to  the  Council  of  the  Geographical 
Society  for  permission  to  reproduce  the  illustration 
of  a  Spinifex  desert ;  the  illustration  in  this  work  is 
from  a  copy  (made  by  my  sister,  Miss  C.  Marr)  of 
the  figure  in  the  Geographical  Journal.  Mr.  A.  W. 
Rogers,  of  the  Geological  Survey  of  Cape  Colony, 
kindly  sent  me  the  photograph  from  which  the  plate 
of  the  Langebergen  Mountains  is  taken,  and  Mr. 
R.  D.  Oldham,  of  the  Geological  Survey  of  India, 
that  from  which  the  plate  showing  the  lake  in 
the  Garo  Hills  is  copied.  The  plate  illustrating 
Ingleborough  Cave  is  from  a  photograph  by  Mr. 
G.  Towler,  of  Settle,  Yorkshire,  and  that  of  the 
Wastwater  Screes  from  one  by  Mr.  Herbert  Bell, 
of  Ambleside.  The  other  plates  are  reproductions 
of  photographs  by  Mr.  E.  J.  Garwood,  to  whom  I 
offer  my  special  thanks.  In  conclusion,  I  desire  to 
express  my  indebtedness  to  a  friend  for  kindly 
reading  the  proofs  of  my  book. 

J.  E.  M. 

CAMBRIDGE,  September,  1899 


TABLE    OF   CONTENTS 

CHAPTER   I. 

INTRODUCTION. 
Scope  of  the  Study — Attributes  of  Scenery       .  .        .  Pages  1-7 

CHAPTER   II. 

OF  THE   NATURE  OF  THE  EARTH'S  EXTERIOR. 
Lithosphere,     Hydrosphere,     and    Atmosphere  —  Rocks — 

Divisional  Planes  of  Rocks       .  ,\  .          8-19 

CHAPTER    III. 

PRODUCTION  OF  DOMINANT   FORMS. 
Accumulation    of    Material — Elevation    and    Depression — 

Sculpture     .  *  .  .  .  20-28 

CHAPTER   IV. 

THE    ATMOSPHERE. 
Colour — Clouds — Cyclones  and  Anti-Cyclones .  .         .         29-45 

CHAPTER   V. 

CONTINENTS  AND  OCEAN  BASINS. 
Production  and  General  Structure  of  Continents  and  Ocean 

Basins — Initiation  of  River  Drainage         .  .         .         46-54 

CHAPTER   VI. 

MOUNTAINS. 
Classification   of   Mountains — Folded    Mountains— Faulted 

Mountains  .  .  .  .  55-69 

CHAPTER   VII. 

MOUNTAINS  (continued}. 
Formation  of  Watersheds— The  Processes  of  Denudation     .         70-93 


viii 


TABLE   OF  CONTENTS 


CHAPTER  VIII. 
MOUNTAINS  (continued}. 

Details  of  Mountain  Structure— Influence  of  the  Sculpturing 
Agents— Influence  of  Rock  Composition  and  Structure 
—Vegetation  on  Mountains  .  .  •  Pages  94-112 

CHAPTER    IX. 

VALLEYS. 
Classification  of  Valleys— Angles  of  Valley  Slopes— Valleys 

of  Erosion  .  .  .  ...     "3-138 

CHAPTER   X. 
VALLEYS  (continued}. 
Complications  of  River  Drainage— Waterfalls— Underground 

Rivers         .  .  .  ...     I39-I57 

CHAPTER  XI. 

LAKES. 

Classification  of  Lakes — Lakes  formed  by  Accumulation  of 
Material— Lakes  formed  by  Earth  Movement— Crater 
Lakes — Lakes  formed  by  Erosion  .  .  .  158-187 

CHAPTER  XII. 
LAKES  (continued). 
Topographical  Features  of  Lake  Shores  and  Lake  Basins — 

Islands  in  Lakes— Colour  of  Lakes  .  .         .     188-202 

CHAPTER   XIII. 

VOLCANOES. 

Theories  of  Vulcanicity — Outlines  and  Structures  of  Vol- 
canoes— Fissure  Eruptions — Geysers — Mud  Volcanoes — 
Earthquakes  .  .  ...  203-230 

CHAPTER  XIV 

PLAINS  AND  PLATEAUX. 

Formation  and  Characters  of  Plains — Formation  and  Charac- 
ters of  Plateaux  .  .  ...  231-247 

CHAPTER   XV. 

DESERTS. 
Production  of  Deserts — Erosion  of  Deserts — Accumulation 

in  Deserts — Vegetation  of  Deserts  .  .        .     248-271 


TABLE   OF   CONTENTS  ix 

CHAPTER   XVI. 

FROST,   SNOW,   AND   ICE. 
Hoar-frost — Snow — Glaciers  .  .  .   Pages  272-296 

CHAPTER   XVII. 

GLACIERS   AND   ICE-SHEETS   OF  VARIOUS   REGIONS. 
Norway — Spitsbergen — Alaska — Greenland      .  .         .     297-309 

CHAPTER   XVIII. 

THE  SIGNS   OF   FORMER  GLACIATION. 
Glacial  Erosion — Glacial  Accumulations  and  Deposits          .     310-320 

CHAPTER   XIX. 

THE  OCEANS. 

Oceanic  Erosion — Formation  of  Coast-lines — Oceanic  Islands 
— Raised  Sea-margins — Marine  Vegetation — Ice  in  the 
Ocean  .  .  .  ...  321-351 

CHAPTER   XX. 
CONCLUSION      .  .  .  ...    352-361 

INDEX  .  .  .  ...     363-368 


LIST   OF   ILLUSTRATIONS 


King's  Bay  Glacier,  Spitsbergen              .  '  .        .    Frontispiece 

Upper  Surface  of  Cloud  in  Eden  Valley  .    To  face  page    21 

Langebergen,  Mossel  Bay  District          .  .  ,,  86 

Nunatak,  Nordenskjold  Glacier               .  .  „  90 

Hornsund  Tind         .                .                .  .  ,,  109 

The  Drei  Zinnen       .                .           .     .  .     •       „  109 

The  Matterhorn,  from  the  Hornli           .  .  „  in 

High  Force,  Teesdale               .                .  -.  ,,  150 

Ingleborough  Cave,  Clapham,  Yorks      .  •  »  156 

The  Ober-Gabelhorn  from  the  Schwarz  See  .  ,,  159 

Marjelen  See             .                .                .  ,,  161 

Sty  Head  Tarn          .                 .                 .  .  ,,  166 

Haweswater               .                .  .  ,,  169 

Smallwater                 .                ...  „  169 

Lago  dell'  Inferno     .                 .                 .  .  ,,  175 

Earthquake-lake,  Garo  Hills    .                 .  .  ,,  180 

The  Screes,  Wast  water             .                .  .  „  196 

Spinifex  :   Queen  Victoria  Desert,  Western  Australia         , ,  268 

Ice-fall  on  Glacier  below  Scerscen  and  Roseg,  Engadine  , ,  286 

Baldhead  and  Booming  Glaciers,  Spitsbergen  .  ,,  299 

Englacial  River,  King's  Glacier,  Spitsbergen  .  ,,  302 


THE   SCIENTIFIC   STUDY 
OF   SCENERY 

CHAPTER  I. 
INTRODUCTION 

A  WIDESPREAD  appreciation  of  the  beauties 
of  nature  is  not  the  least  of  the  many  beneficent 
changes  which  have  marked  the  Victorian  era,  and 
with  this  appreciation  has  sprung  up  a  desire  on 
the  part  of  many  people  to  obtain  some  insight  into 
the  causes  of  scenery.  Few  persons  at  the  present 
day  are  content  to  believe  that  the  superficial  features 
of  the  earth  have  always  been  as  they  are  now,  and 
the  wish  to  know  something  of  the  changes  which 
are  responsible  for  the  production  of  the  existing 
features  of  the  globe  is  a  very  natural  one,  and  its 
fulfilment  not  only  affords  additional  pleasure  to  a 
vast  number  of  lovers  of  scenery,  but  gives  them  an 
insight  into  a  noble  aim  of  the  natural  sciences 
which  is  too  often  overlooked.  These  sciences  are 
too  frequently  regarded  from  a  purely  philosophical 
or  a  merely  economic  standpoint,  and  their  aesthetic 
side  is  ignored,  though  this  is  very  valuable  as  a 
means  of  education. 


2       SCIENTIFIC   STUDY   OF  SCENERY 

The  scientific  study  of  scenery  is  concerned  with 
all  the  existing  features  of  earth,  sky,  and  sea,  which 
are  visible  to  the  eye,  quite  apart  from  their  relative 
attractiveness,  which  is  indeed  often  a  matter  of 
individual  taste,  for  a  view  which  one  person  con- 
siders tame  and  uninteresting  will  produce  feelings 
of  profound  satisfaction  in  another.  It  is  well  known 
that  mountains  which  are 'now  attractive  to  so  many 
were  generally  regarded  with  repulsion  or  horror  at 
no  remote  period ;  while  a  fenland  flat  which  arouses 
little  enthusiasm  in  some  is  contemplated  with  in- 
tense pleasure  by  others. 

If  we  take  this  comprehensive  view  of  the  scope 
of  our  study,  it  will  be  seen  that  it  covers  a  large 
portion  of  the  field  of  physical  geography ;  and 
indeed  no  better  method  of  imparting  the  elementary 
principles  of  physical  geography  exists  than  that  of 
teaching  the  student  the  significance  of  the  earth's 
superficial  features,  especially  those  of  the  districts 
with  which  he  is  acquainted.  When  this  is  recog- 
nised, physical  geography  will  take  its  proper  place 
as  a  subject  eminently  adapted  for  schools,  and  as 
an  introduction  to  a  knowledge  of  geology  of  far 
greater  interest  to  the  bulk  of  educated  persons  than 
the  dry  details  concerning  rocks  and  fossils  which 
are  frequently  supplied  to  them  as  an  introduction 
to  the  science,  details  which  naturally  cause  them 
to  turn  away  from  the  pursuit  of  the  study  with  a 
feeling  of  aversion. 

In  viewing  any  scene,  the  attributes  which  strike 
us  specially  are  size,  form,  character,  surface,  colour, 
and  movement,  and  of  these  attributes  there  is  little 
doubt  that  form  is  by  far  the  most  important,  and 
it  will  be  most  attentively  considered  in  this  work, 


INTRODUCTION  3 

though  occasional  references  will  necessarily  be  made 
to  other  attributes.  The  importance  of  form  is  so 
great  that  it  is  necessary  to  devote  a  few  words  to 
its  consideration,  but  this  will  best  be  done  by 
quoting  the  words  of  acknowledged  masters  of  the 
study  of  scenery.  Thus  Ruskin  writes :  "  We  shall 
see  hereafter,  in  considering  ideas  of  beauty,  that 
colour,  even  as  a  source  of  pleasure,  is  feeble  com- 
pared with  form";1  while  concerning  magnitude 
Wordsworth  observes  that  "  a  short  residence  among 
the  British  mountains  will  furnish  abundant  proof, 
that,  after  a  certain  point  of  elevation  ...  the  sense 
of  sublimity  depends  more  upon  form  and  relation 
of  objects  to  each  other  than  upon  their  actual 
magnitude."2 

As  the  four  attributes  size,  colour,  movement,  and 
character  of  surface,  or,  as  we  may  term  the  last, 
texture,  will  not  be  treated  systematically,  it  will  be 
convenient  at  this  point  to  make  a  few  further 
observations  concerning  them. 

I.  Size, — It  is  evident  that  mere  size  cannot  add 
directly  to  the  beauty  of  an  object  or  group  of 
objects,  and  the  influence  of  magnitude  of  natural 
objects  is  dependent  upon  the  imagination.  The 
truth  of  this  statement  is  well  illustrated  by  an 
example  given  by  Ruskin,  which  I  may  be  pardoned 
for  quoting  at  length  : — 

"Not  long  ago,  as  I  was  leaving  one  of  the  towns  of 
Switzerland,  early  in  the  morning,  I  saw  in  the  clouds 
behind  the  houses  an  Alp  which  I  did  not  know,  a  grander 
Alp  than  any  I  knew,  nobler  than  the  Schreckhorn  or  the 

1  Modern  Painters,  vol.  i.,  part  ii.,  sec.  i.,  chap.  v. 

2  A    Complete   Guide  to  the  Lakes,   .   ,   .   with  Mr.    Wordsworth's. 
Description  of  the  Scenery  of  the  Country,  sec.  iv. 


4      SCIENTIFIC   STUDY   OF   SCENERY 

Monch;  terminated,  as  it  seemed,  on  one  side  by  a 
precipice  of  almost  unimaginable  height;  on  the  other, 
sloping  away  for  leagues  in  one  field  of  lustrous  ice,  clear 
and  fair  and  blue,  flashing  here  and  there  into  silver  under 
the  morning  sun.  For  a  moment  I  received  a  sensation  of 
as  much  sublimity  as  any  natural  object  could  possibly  excite; 
the  next  moment,  I  saw  that  my  unknown  Alp  was  the  glass 
roof  of  one  of  the  workshops  of  the  town  rising  above  its 
nearer  houses  and  rendered  aerial  and  indistinct  by  some 
pure  blue  wood  smoke  which  rose  from  intervening  chimneys. 
"  It  is  evident,  that  so  far  as  mere  delight  of  the  eye  was 
concerned,  the  glass  roof  was  here  equal,  or  at  least  equal 
for  a  moment,  to  the  Alp.  Whether  the  power  of  the 
object  over  the  heart  was  to  be  small  or  great,  depended 
altogether  upon  what  it  was  understood  for,  upon  its  being 
taken  possession  of  and  apprehended  in  its  full  nature, 
either  as  a  granite  mountain  or  a  group  of  panes  of  glass ; 
and  thus,  always,  the  real  majesty  of  the  appearance  of  the 
thing  to  us,  depends  upon  the  degree  in  which  we  our- 
selves possess  the  power  of  understanding  it.  ...  For 
though  the  casement  had  indeed  been  an  Alp,  there  are 
many  persons  on  whose  minds  it  would  have  produced  no 
more  effect  than  the  glass  roof.  It  would  have  been 
to  them  a  glittering  object  of  a  certain  apparent  length 
and  breadth,  and  whether  of  glass  or  ice,  whether  twenty 
feet  in  length,  or  twenty  leagues,  would  have  made  no 
difference  to  them ;  or,  rather,  would  not  have  been  in  any 
wise  conceived  or  considered  by  them.  Examine  the 
nature  of  your  own  emotion  (if  you  feel  it)  at  the  sight  of 
the  Alp,  and  you  find  all  the  brightness  of  that  emotion 
hanging,  like  dew  on  gossamer,  on  a  curious  web  of  subtle 
fancy  and  imperfect  knowledge."1 

II.  Colour. — It  would  be  impossible  in  a  work  like 
the  present  to  give  a  lengthy  account  of  the  infinite 

1  Modern  Painters,  vol.  iii.,  part  iv.,  chap.  x. 


INTRODUCTION  5 

variations  in  colouring  produced  by  different  atmo- 
spheric conditions,  though  something  will  be  said 
upon  this  subject  when  we  consider  the  atmosphere. 
But  beyond  this  variation  we  find  definite  colours 
associated  with  particular  objects,  and  these  often 
play  an  important  part  in  affecting  the  aspect  of  a 
scene.  For  instance,  the  colour  of  pure  water  is 
stated  to  be  a  greenish  blue,  as  will  be  more  fully 
described  when  treating  of  expanses  of  water.  The 
colour  of  terrestrial  surfaces  is  largely  affected  by  the 
nature  of  the  vegetation  as  well  as  by  that  of  the 
rocks.  Though  foliage  has  a  more  general  effect  than 
flowers  in  giving  colour  to  landscape,  the  influence 
of  the  latter  is  by  no  means  small.  The  vivid  scarlet 
of  Poppy  land,  the  purple  tracts  of  heather  in  High- 
land districts,  the  richly  coloured  carpet  of  flowers 
in  Alpine  meadows  before  the  hay  is  cut,  are  cases 
where  a  marked  effect  is  produced.  The  foliage  of 
trees  and  grasses  need  only  be  mentioned,  though  of 
the  latter  it  may  be  remarked  that  the  most  striking 
effects  are  produced  in  rainy  regions.  The  brilliant 
green  of  our  Lakeland  vales  is  due  to  the  excessive 
rainfall,  which  in  more  ways  than  one  must  be 
accounted  beneficial  to  the  lover  of  scenery.  It  is 
to  lowlier  vegetation  that  we  are  indebted  for  some 
of  our  richest  colouring.  The  changes  which  occur 
in  the  bracken  of  Westmorland  are  thus  described  by 
Wordsworth : — 

"  When  in  the  heat  of  advancing  summer,  the  fresh  green 
tint  of  the  herbage  has  somewhat  faded,  it  is  again  revived 
by  the  appearance  of  the  fern  profusely  spread  over  the 
same  ground ;  and,  upon  this  plant,  more  than  upon  any- 
thing else,  do  the  changes  which  the  seasons  make  in  the 
colouring  of  the  mountains  depend.  About  the  first  week 


6      SCIENTIFIC   STUDY   OF  SCENERY 

in  October,  the  rich  green,  which  prevailed  through  the 
whole  summer,  is  usually  passed  away.  The  brilliant  and 
various  colours  of  the  fern  are  then  in  harmony  with  the 
autumnal  woods  :  bright  yellow  or  lemon-colour,  at  the  base 
of  the  mountains,  melting  gradually,  through  orange,  to  a 
dark  russet-brown  towards  the  summits,  where  the  plant, 
being  more  exposed  to  the  weather,  is  in  a  more  advanced 
state  of  decay." l 

The  same  writer  refers  to  the  effect  of  the 
lichens,  which  is  also  thus  beautifully  described  by 
Ruskin  : — 

"As  in  one  sense  the  humblest,  in  another  they  are  the 
most  honoured  of  the  earth-children.  Unfading,  as  motion- 
less, the  worm  frets  them  not,  and  the  autumn  wastes  not. 
Strong  in  lowliness,  they  neither  blanch  in  heat  nor  pine 
in  frost.  To  them,  slow-fingered,  constant-hearted,  is 
entrusted  the  weaving  of  the  dark,  eternal  tapestries  of 
the  hills;  to  them,  slow  -  pencilled,  iris-dyed,  the  tender 
framing  of  their  endless  imagery.  Sharing  the  stillness  of 
the  unimpassioned  rock,  they  share  also  its  endurance ; 
and  while  the  winds  of  departing  spring  scatter  the  white 
hawthorn  blossom  like  drifted  snow,  and  summer  dims  on 
the  parched  meadow  the  drooping  of  its  cowslip-gold, — far 
above,  among  the  mountains,  the  silver  lichen-spots  rest, 
star-like,  on  the  stone ;  and  the  gathering  orange  stain  upon 
the  edge  of  yonder  western  peak  reflects  the  sunsets  of  a 
thousand  years."2 

But  though  the  colouring  of  rocks  as  seen  in 
nature  is  so  often  due  to  vegetation  upon  their 
surface,  the  bare  rock  frequently  possesses  colour 
of  its  own,  owing  to  the  presence  of  organic  matter, 
or  of  some  compound  of  iron.  The  former  usually 

1  WORDSWORTH,  loc.  cit.,  sec.  i. 

*  RUSKIN,  Modern  Painters,  vol.  v.,  part  vi.,  chap.  x. 


INTRODUCTION  7 

gives  a  grey-blue  or  black  colour,  while  the  colouring 
due  to  iron  varies  according  to  the  particular  com- 
pound which  is  present.  The  peroxide  of  iron 
produces  a  rich  red,  so  well  known  in  the  red 
sandstones  of  Britain,  the  hydrated  oxide  gives 
yellow,  orange,  or  rust-brown  hues,  while  the  silicate 
is  green.  The  effect  due  to  colouring  matter  in  the 
rocks  is  specially  well  brought  out  in  desert  regions 
where  the  vegetation  is  scanty ;  for  instance,  it  is 
very  noticeable  in  the  walls  of  the  deep  canons  of 
the  western  territories  of  North  America. 

III.  Texture. — The  important  influence  of  texture 
is  well  illustrated  by  the  frequency  of  such  expres- 
sions as  "  fleecy  clouds,"   "  an  oily  sea,"   "  soft   and 
downy   pasturage,"    in    descriptions    of  scenery.     It 
is  largely  determined  by  differences  of  shape,  which 
are  too  minute  to  be  detected  in  detail,  though  they 
produce  a  general  effect  upon  the  surface  which  is 
viewed,  and  on  this  account  it  is  superfluous  to  do 
more  than  call  attention  to  this  attribute  of  surfaces 
as   affecting   scenes.     Lustre   largely  depends   upon 
the   texture   of  surfaces,  and   may  be  conveniently 
regarded  under  this  head. 

IV.  Movement. — The   effect   of  movement  in  air, 
on  water,  or  on  land  is  often  very  noticeable  as  an 
attribute  of  a  scene  which   may  produce  a  feeling 
of  exhilaration  in  the  mind  of  the  beholder.     It  is 
only  necessary  to  refer  to  the  effect  of  moving  cloud, 
of  the  eddying  torrent,  the  sea-wave,  and  the  waving 
vegetation  of  cornfield,  down,  or  mountain-brow  as 
illustrations  of  the  influence  of  motion  upon  scenery. 


CHAPTER  II. 

OF  THE  NATURE  OF  THE  EARTH'S  EXTERIOR 

THE  unknown  interior  of  the  earth  is  surrounded 
by  three  envelopes,  the  lithosphere,  hydro- 
sphere, and  atmosphere,  of  which  the  first  and  third 
are  continuous,  while  the  second  is  interrupted  in 
places,  and  allows  portions  of  the  first  to  project 
upwards  into  the  third.  The  lithosphere  is  that 
portion  of  the  earth  which  is  popularly  spoken  of 
as  its  crust,  and  is  in  the  solid  condition ;  the 
hydrosphere  is  liquid,  and  is  composed  of  the  oceans, 
rivers,  lakes,  and  indeed  all  the  surface  waters  of  the 
globe;  the  atmosphere  is  the  gaseous  envelope 
which  surrounds  the  lithosphere  and  hydrosphere, 
and  extends  for  an  unknown  but  limited  distance 
outward  from  their  surfaces.  Portions  of  these 
envelopes  are  capable  of  passing  from  one  state 
to  another ;  for  instance,  parts  of  the  waters  of 
the  hydrosphere  enter  into  the  composition  of  the 
lithosphere,  or  as  aqueous  vapour  pass  into  the 
atmosphere ;  fragments  of  lithosphere — e.g.,  volcanic 
dust— are  often  suspended  for  a  long  period  in  the 
atmosphere,  while  the  gases  of  the  atmosphere  are 
taken  up  by  the  earth's  crust  and  the  waters  of  the 
j  globe.  This  power  which  the  envelopes  possess  of 
I  interchanging  some  of  their  components  will  be 


NATURE  OF  EARTH'S  EXTERIOR   9 

found  to  exercise  a  marked  influence  upon  scenic 
effects. 

It  is  unnecessary  at  present  to  touch  more  fully 
upon  the  characteristics  of  atmosphere  and  hydro- 
sphere, but  the  nature  of  the  lithosphere  requires 
further  consideration  at  this  initial  stage  of  our 
inquiries,  for  the  features  of  the  globe  are  notably 
affected  by  the  composition  and  structure  of  the 
earth's  crust. 

The  lithosphere  is  composed  of  rocks,  which  are 
aggregates  of  mineral  particles,  the  term  rock  being 
used  quite  irrespectively  of  any  consideration  of  hard- 
ness or  coherence.  Thus  a  geologist  would  speak  of 
the  loose  sand  of  the  sea-shore  as  a  rock  equally  with 
the  hardest  granite  or  basalt.  Rocks  are  divided 
into  two  great  classes.  Thejgneous  class  consists  of 
rocks  which  have  directly  consolidated  from  a  state  of 
fusion,  while  the  derivative  class  has  been  formed 
by  accumulation  of  material  on  the  surface  of  the 
earth,  that  material  not  having  been  in  a  state  of 
fusion  immediately  before  its  accumulation.  These 
derivative  rocks  may  be  composed  of  materials 
derived  from  the  atmosphere  (as  carbonaceous 
accumulations  such  as  peat  and  coal,  formed  of 
carbon  compounds  extracted  by  vegetation  from 
the  atmosphere,  and  ice  derived  from  the  aqueous 
vapour  of  the  atmosphere),  or  they  may  be  formed 
of  substances  previously  contained  in  solution  in  the 
waters  of  the  hydrosphere,  and  brought  into  the 
solid  condition  by  precipitation  or  by  the  agency  of 
organisms  (for  instance,  rock-salt,  gypsum,  and  many 
limestones  and  siliceous  deposits),  or  they  may 
consist  of  fragments  broken  from  pre-existing  rocks 
and  carried  by  mechanical  means  to  the  position  in 


io     SCIENTIFIC   STUDY   OF  SCENERY 

which  they  are  accumulated  (as  sandstone  and  mud), 
or  they  may  be  due  to  a  combination  of  two  or  all  of 
these  processes.  The  great  bulk  of  the  derivative 
rocks  are  accumulated  in  layers  (generally,  though 
not  universally,  at  the  bottom  of  sheets  of  water), 
and  hence  they  are  frequently  spoken  of  as  stratified 
rocks. 

Igneous  and  stratified  rocks  alike  may  undergo 
considerable  changes  after  their  formation,  and  these 
changes  are  spoken  of  as  metanwrphic,  and  we  meet, 
therefore,  with  metamorphic  igneous  as  well  as 
metamorphic  aqueous  rocks. 

In  the  following  chapter  we  shall  call  attention  to 
the  operations  of  certain  agents  which  are  responsible 
for  the  sculpture  of  the  rocks  of  the  earth's  crust, 
and  before  studying  these  operations  it  is  necessary 
to  allude  to  various  characteristics  of  rocks  which 
influence  the  sculpturing  processes. 

If  all  rock  had  the  same  composition,  and  was 
absolutely  homogeneous  throughout,  the  agents 
which  affect  it  would  do  so  over  the  entire  surface 
in  the  same  manner,  assuming  that  these  agents 
worked  uniformly,  but  a  very  brief  inspection  of  the 
crust  of  the  globe  shows  that  the  work  is  not  per- 
formed in  a  uniform  manner,  even  under  conditions 
in  which  the  agents  can  work  uniformly,  and  accord- 
ingly it  is  clear  that  rocks  differ  from  one  another 
in  certain  respects,  some  being  more  durable  than 
others.  Some  of  the  differences,  such  as  difference 
of  chemical  composition,  may  be  discovered  in  a  hand 
specimen.  This  difference  may  be  complete  as 
between  chalk  and  flint,  the  former  being  composed 
of  carbonate  of  lime,  the  latter  of  silica,  or  it  may 
be  partial  as  between  a  calcareous  sandstone  and  a 


NATURE  OF  EARTH'S  EXTERIOR  n 

ferruginous  sandstone,  one  possibly  composed  of 
grains  of  silica  cemented  by  carbonate  of  lime,  the 
other  of  grains  of  the  same  material  with  a  cement 
of  oxide  of  iron.  As  some  of  these  constituents  are 
very  soluble  in  ordinary  water,  others  less  soluble, 
and  others  again  practically  insoluble,  it  is  clear  that 
the  influence  of  water  upon  rocks  of  different  com- 
position may  produce  very  different  results. 

Other  differences  may  be  observed  in  a  hand 
specimen  between  rocks  of  the  same  composition. 
Thus  a  siliceous  rock  may  be  practically  homo- 
geneous, like  flint,  or  it  may  be  composed  of  a 
number  of  grains  cemented  into  a  more  or  less  hard 
sandstone.  Mechanical  differences  of  this  nature, 
which  are  readily  observable  in  a  hand  specimen, 
may  be  spoken  of  as  differences  of  texture. 

Again,  when  we  examine  the  rocks  of  a  country 
we  shall  certainly  find  differences  which  are  not 
easily  detected,  if  at  all,  in  a  hand  specimen.  Among 
the  most  noticeable  are  the  divisional  planes  which 
cause  rocks  to  break  more  readily  in  one  direction 
than  another.  These  may  be  spoken  of  as  differences 
of  structure.  As  these  structural  differences  play  a 
most  important  part  in  determining  and  controlling 
the  action  of  the  agents  of  sculpture,  it  is  necessary 
to  treat  of  them  at  some  length. 

To  the  geologist  the  difference  between  divisional 
planes  is  of  prime  importance,  mainly  with  regard  to 
the  way  in  which  they  are  produced,  though  for  our 
present  purpose  their  importance  is  commensurate 
with  their  effect  upon  superficial  features ;  but  as  the 
planes  produced  in  any  one  way  generally  give  rise 
to  similar  effects,  which  differ  from  those  caused  by 
planes  produced  otherwise,  it  is  quite  convenient  to 


12     SCIENTIFIC   STUDY   OF   SCENERY 

classify  these  planes  according  to  their  origin,  and 
they  may  be  grouped  under  three  heads  :— (i)  Planes 
formed  during  the  formation  of  the  rocks ;  (ii)  those 
formed  after  formation  by  fracture;  (iii)  those  pro- 
duced by  metamorphism.  It  is  not  easy  in  all  cases 
to  distinguish  between  (ii)  and  (iii),  but  there  is  no 
difficulty  in  effecting  a  practical  separation  between 
the  two. 

In  class  (i)  we  place  planes  of  stratification  and 
lamination,  in  (ii)  joint-planes  and  fault-planes,  and  in 
(iii)  cleavage-planes  and  planes  of  foliation.  Between 
these  planes  we  may  now  proceed  to  discriminate. 

(a)  Planes  of  Stratification  and  Lamination. — It  is 
found  as  the  result  of  observation  that  stratified 
rocks  are  accumulated  in  layers,  which  are  separated 
by  divisional  planes;  these  when  the  rocks  are 
formed  lie  generally  in  a  horizontal  position. 
These  planes  are  planes  of  stratification,  or  when 
they  are  near  together  (say  several  in  the  thickness 
of  an  inch  of  deposit)  planes  of  lamination,  the  latter 
being  merely  planes  of  stratification  on  a  small  scale. 
A  plane  of  stratification,  then,  separates  two  beds  or 
strata  of  rock.  It  need  not  necessarily  be  a  plane  of 
discontinuity,  but  may  merely  separate  two  beds  of 
different  composition,  as  mud  and  limestone,  which 
are  nevertheless  welded  together,  but  the  majority  of 
planes  of  stratification,  and  those  with  which  we  are 
here  chiefly  concerned,  are  actual  planes  of  discon- 
tinuity along  which  rocks  may  be  split.  It  is  obvious 
that  these  planes  are,  strictly  speaking,  absent  from 
igneous  rock,  but  similar  planes  mayseparate  lava  flows 
from  sediments  which  overlie  or  underlie  them,  and  we 
may  conveniently  include  such  planes  in  this  division. 

It  was  stated  above  that  planes  of  stratification  are 


NATURE  OF  EARTH'S  EXTERIOR  13 

usually  formed  as  horizontal  planes,  but  they  are 
frequently  found  at  all  angles  and  even  turned  over, 
so  that  a  bed  which  was  once  lower  now  lies  above 
the  original  upper  one.  It  is  known  that  this  is  the 
result  of  movements  of  the  earth's  crust  occurring 
subsequently  to  the  deposition  of  the  strata,  which 
have  produced  a  series  of  folds.  A  few  words  must 
be  devoted  to  the  nomenclature  applied  to  these 
disturbed  strata. 

The  greatest  angle  which  an  inclined  stratum 
makes  with  the  horizon  is  known  as  the  angle  of 
dip  of  the  stratum,  and  the  direction  in  which  the 
stratum  plunges  down  into  the  crust  along  the  line 
of  this  greatest  angle  is  the  direction  of  dip. 
Imagine  that  the  roof  of  a  house  whose  ridge  runs 
north  and  south  is  composed  of  a  bent  bed.  Then 
the  dip  is  east  on  one  side  and  west  on  the  other, 
and  if  the  greatest  angle  of  the  slope  is  30°,  the  bed 
would  be  said  to  dip  to  the  east  or  west  at  30°.  A 
horizontal  line  at  right  angles  to  the  direction  of  dip 
is  known  as  the  line  of  strike  of  the  beds.  Thus, 
in  the  above  example,  the  ridge  of  the  roof  lies  along 
the  line  of  strike,  which  is  always  at  right  angles 
to  the  direction  of  greatest  inclination,  along  which 
a  stream  of  water  would  flow  if  it  were  poured  upon 
the  surface  of  the  bed.  The  line  along  which  a  plane 
of  stratification  (or  a  plane  of  joint,  fault,  cleavage, 
or  foliation)  comes  to  the  surface  of  the  ground  is 
spoken  of  as  its  outcrop,  and  the  outcrop  of  the 
stratum  is  when  the  bed  itself  comes  to  the  surface, 
in  this  case  not  as  a  line,  but  as  a  narrow  belt 
bounded  by  approximately  parallel  lines  of  stratifi- 
cation, and  a  bed  or  divisional  plane  is  spoken  of 
as  cropping  out  along  such  a  belt  or  line. 


i4    SCIENTIFIC   STUDY   OF   SCENERY 

The  folds  into  which  inclined  strata  are  thrown 
are  known  to  geologists  by  different  names  accord- 
ing to  their  character,  but  it  will  be  convenient  to  use 
less  technical  terms  in  the  body  of  the  work,  though 
the  technical  names  are  given  here  for  purposes  of 
reference.  Fig.  I  shows  the  character  of  some  of 
these  folds. 

When  the  strata  dip  away  on  either  side  from 
an  axis  the  structure  may  be  termed  a  saddle 
(anticline],  as  in  A  I  of  figure,  while  when  they  dip 
towards  an  axis,  as  in  A  2,  we  have  a  trough  (syncline). 
When  strata  are  horizontal,  then  dip  in  any  direction, 
and  once  more  become  horizontal,  we  get  a  hogback 
(monocline],  .as  in  A  3.  B  I  and  B  2  show  the 
method  in  which  the  strata  of  a  saddle  and  trough 
crop  out  upon  a  flat  surface  (if  the  top  of  the  fold  be 
cut  off).  The  arrow  indicates  the  direction  of  the 
dip,  and  the  numbers  the  angle.  Thus  the  axes  of 
the  saddle  and  trough  here  run  north  and  south, 
and  the  beds  dip  at  an  angle  of  45°  east  and  west, 
away  from  the  axis  in  the  former  figure,  towards  it 
in  the  latter.  If  the  strata,  instead  of  being  folded 
around  an  axial  line,  are  folded  round  a  point,  the 
saddle  is  replaced  by  a  dome  (B  3),  and  the  trough 
by  a  basin  (B  4).  It  will  be  seen  that  the  section 
across  a  dome  is  similar  to  that  across  a  saddle  at 
right  angles  to  its  axis,  and  that  of  a  basin  to  that 
of  a  trough,  though  the  outcrop  of  the  beds  in  plan 
is  different.  In  nature  the  domes  and  basins  are 
usually  somewhat  unsymmetrical,  and  we  get  every 
gradation  from  the  ideal  saddles  and  troughs  to  the 
symmetrical  domes  and  basins.  When  a  fold  con- 
sisting of  saddle  and  trough  has  been  continued 
until  the  central  part  has  been  turned  over,  as  in 


i6     SCIENTIFIC   STUDY   OF   SCENERY 

A  4  (Fig.  i),  so  that  in  that  part  the  stratum  b, 
originally  below,  now  rests  upon  the  stratum  a,  the 
fold  is  termed  an  overfold. 

(b)  Joint-planes. — In  addition  to  the  planes  of 
stratification  which  separate  strata,  we  often  find  a 
number  of  more  or  less  regular  planes  running  at 
different  angles  to  the  stratification  -  planes,  and 
similar  planes  are  found  in  igneous  rocks.  They 
may  be,  and  in  many  cases'  have  been,  produced  in 
different  ways,  but  it  is  not  our  province  to  consider 
their  mode  of  production.  They  clearly  differ  from 
the  planes  of  stratification,  and  there  is  this  important 
difference  between  them  and  cleavage -planes,  that, 
whereas  the  rock  between  two  contiguous  joint-planes 
shows  no  tendency  to  split  parallel  to  the  joint- 
planes,  that  between  adjoining  cleavage-planes  in 
a  fragment  of  a  cleaved  rock  may  be  split  up  into 
extremely  thin  plates,  whose  surfaces  run  parallel 
with  the  two  cleavage  faces  with  which  we  com- 
menced ;  indeed,  with  delicate  tools,  the  splitting 
process  may  be  carried  on  almost  indefinitely.  The 
joints  are  often  very  irregular,  but  we  frequently  find 
the  more  important  ones  running  with  a  considerable 
degree  of  regularity.  The  columnar  jointing  of  basalt 
and  other  rocks  is  somewhat  rare,  and  need  not  be  now 
considered,  but  both  igneous  and  aqueous  rocks  often 
show  parallel  systems  of  joints,  which  allow  the  rock 
to  be  broken  with  comparative  ease  into  rectangular 
masses.  These  joints  are  termed  master-joints.  In 
igneous  rocks  three  sets  of  master-joints,  each  at 
right  angles  to  the  other  two,  must  exist,  in  order 
that  the  rock  may  be  separated  into  rectangular 
blocks.  In  stratified  rocks  the  planes  of  stratification 
already  form  one  set  of  planes  of  weakness,  and  these 


NATURE  OF  EARTH'S  EXTERIOR  17 

rocks  may  be  separated  into  rectangular  blocks  if 
two  sets  of  joints  exist.  When  the  strata  are 
horizontal  the  master-joints  tend  to  be  vertical  and 
at  right  angles  to  one  another.  Thus  if  one  set 
runs  north  and  south  the  other  will  run  east  and 
west. 

Very  important  to  us  is  the  relationship  which 
frequently  exists  between  the  direction  of  the  dip 
and  strike  of  inclined  strata  and  that  of  the  master- 
joints.  One  set  usually  runs  parallel  to  the  line  of 
strike,  the  other  in  the  direction  of  dip,  the  former 
being  termed  strike-joints  and  the  latter  dip-joints. 
Of  these  the  strike-joints  are  usually  more  important 
than  those  parallel  to  the  dip  ;  also  the  planes  of  the 
strike-joints  in  inclined  strata  will  in  most  cases  be 
approximately  at  right  angles  to  the  planes  of  the 
strata.  Thus  if  the  strata  dip  at  30°  to  the  east 
the  strike-joints  may  slope  downwards  towards  the 
west  at  an  angle  of  60°. 

(c)  Fault-planes. — The  existence  of  strata  thrown 
into  folds  proves  that  in  the  circumstances  in  which 
the  rocks  were  folded  they  had  lost  much  of  the 
rigidity  which  they  normally  possess ;  but,  never- 
theless, in  many  cases  movement  of  the  strata  has 
occurred  in  a  way  which  prevented  the  rocks  from 
being  accommodated  to  the  new  conditions  by 
folding  only,  and  they  have  become  fractured,  and 
the  relative  position  of  the  rocks  on  the  two  sides 
of  the  fracture  has  been  altered,  the  rocks  on  one 
side  having  been  carried  up  or  down  relatively  to 
those  on  the  other  side  of  the  plane  of  fracture, 
giving  rise  to  what  is  known  as  a  fault,  as  illustrated 
in  section  in  Fig.  2,  where  the  portion  of  the  stratum 
c  on  the  right  of  the  section,  which  was  once  con- 


i8     SCIENTIFIC   STUDY   OF  SCENERY 

tinuous  with  c  on  the  left,  has  been  thrown  down,1 
so  that  it  now  abuts  against  another  bed.  The 
fissure  X  Y  is  an  actual  plane  of  discontinuity, 
comparable  with  a  joint-plane,  and  indeed  it  is  a 
joint-plane,  along  which  differential  movement  of 
the  rocks  has  occurred.  Accordingly  we  often  find 
one  set  of  important  faults  which  have  a  trend 
parallel  to  the  strike  of  the  strata  and  another  set 
at  right  angles ;  these  are  strike-faults  and  dip- 
faults.  To  the  student  of  scenery  faults  are  of 


Surface 

of    X        ground 

c 

\ 

e 

—V 

1} 

\ 

C 

g 

V  — 

(I 

h, 

\r 

FIG.  2. 

importance  chiefly  because  they  frequently  cause 
rocks  of  different  degrees  of  durability  to  exist  in 
apposition. 

(d)  Cleavage-planes. — When  rocks  have  been  sub- 
jected to  intense  lateral  compression  the  particles 
of  the  rock  become  flattened  in  the  direction  of 
pressure  and  elongated  in  a  direction  at  right  angles 
to  this,  and  the  rock  has  a  tendency  to  split  into 
thin  plates  at  right  angles  to  the  direction  in  which 
the  pressure  was  applied.  Rocks  which  possess  this 
property  are  known  as  slates,  and  the  planes  along 
which  fission  occurs  are  cleavage-planes.  As  these 

1  The  side  of  the  fault  where  the  strata  are  relatively  lower  is  termed 
the  downthrow  side,  the  opposite  being  the  upthrow  side.  These 
terms  are  used  for  convenience,  without  assuming  that  one  side  has 
been  actually  pushed  downwards  and  the  other  upwards. 


NATURE  OF  EARTH'S  EXTERIOR  19 

planes  are  frequently  parallel  over  wide  regions  and 
often  highly  inclined  to  the  horizon,  cleaved  rocks 
are  very  prone  to  become  affected  by  the  agents  of 
disintegration,  whose  operations  will  be  subsequently 
considered,  and  a  country  occupied  by  slaty  rocks 
often  exhibits  characteristic  scenic  features. 

(e)  Foliation  -planes.  —  Many  metamorphic  rocks 
consist  of  felted  masses  of  crystals,  whose  longer 
axes  lie  parallel,  and  the  rocks  exhibit  a  fissile 
structure,  the  planes  of  fissility  being  also  parallel 
to  the  direction  of  the  longer  axes  of  the  crystals. 
These  rocks  are  termed  schists,  and  the  planes  of 
fissility  are  spoken  of  as  foliation-planes.  There  is 
no  doubt  that  these  rocks  are  closely  related  to 
slates,  which  also  frequently  exhibit  a  crystalline 
structure,  and  we  find  every  gradation  from  slate  to 
schist.  In  some  cases  the  foliation-planes  were 
originally  stratification-planes,  and  in  others  planes 
of  cleavage.  Consequently  the  planes  of  discon- 
tinuity in  schists  are  comparable  with  other  planes, 
and  the  rocks  are  here  placed  in  a  separate  class 
chiefly  on  account  of  their  characteristic  texture, 
owing  to  the  parallelism  of  the  more  or  less  coarsely 
crystalline  components. 

It  will  be  seen  that  the  distinctions  above  given 
enable  the  rocks  to  be  separated  into  classes  closely 
comparable  with  those  adopted  by  Ruskin.  The 
igneous  rocks  largely  contain  his  massive  crystallines, 
the  foliated  rocks  his  slaty  crystallines,  the  cleaved 
rocks  his  slaty  coherents,  and  the  ordinary  stratified 
rocks  his  compact  coherents. 


CHAPTER   III. 
PRODUCTION   OF   DOMINANT  FORMS 

THE    changes  which  produce  the   characteristic 
forms  in  sky,  sea,  and  surface  of  the  solid  land 
are  strictly  comparable  upon  broad  lines,  and  may  be 
separated  into  three  divisions,  namely,  accumulation, 
elevation  and  depression,  and  sculpture. 

Accumulation  is  concerned  with  bringing  together 
of  the  material  which  will  subsequently  be  moulded 
into  the  various  forms  which  delight  the  eye,  whether 
of  cloud,  terrestrial  water-surface,  or  dry  land,  and  in 
each  case  the  effect  of  accumulation  is  to  give  rise  to 
comparatively  level  surfaces,  which,  in  the  absence  of 
other  change,  would  present  a  monotonous  aspect. 
Commencing  with  the  atmosphere,  we  find  that  it  is 
divisible  into  layers  whose  surfaces  are  approximately 
parallel  with  the  earth's  surface,  each  layer,  under 
conditions  of  equilibrium,  having  a  temperature 
differing  from  that  of  the  layers  above  and  beneath, 
and  accordingly  capable  of  retaining  a  different 
amount  of  aqueous  vapour.  When  this  aqueous 
vapour  condenses,  it  tends  to  accumulate  in  level 
layers,  if  the  barometric  and  other  conditions  are 
uniform  over  wide  spaces,  and  accordingly  we  have 
an  accumulation  of  cloud  with  a  flat  upper  surface. 
Turning  to  the  hydrosphere,  as  water  tends  to  seek 


PRODUCTION  OF  DOMINANT  FORMS    21 

its  own  level,  the  sheets  of  water  when  at  rest  have 
also  a  flat  upper  surface.  This  flatness  in  the  case  of 
the  lithosphere  is  caused  by  the  accumulation  of 
stratified  rocks  in  horizontal  layers,  so  that  if  the 
ocean,  which  is  the  great  receptacle  of  sediment, 
continuously  received  deposit,  and  no  other  change 
took  place,  it  would  eventually  be  silted  up,  and 
converted  into  a  level  plane,  whose  surface  would 
coincide  with  that  of  the  present  ocean  surface, 
though,  apart  from  this  complete  silting  up,  a  flat 
surface  is  produced  beneath  the  ocean-top  by  the 
level  deposit  of  material. 

Elevation  and  depression  modify  these  monoto- 
nous surfaces,  diversifying  them  by  the  production 
of  dome  and  basin  or  ridge  and  trough,  the  former 
being  usually  more  local  than  the  latter.  The  ridge 
and  trough  structure  is  due  to  the  formation  of  a 
series  of  waves,  and  air-waves,  water-waves,  and 
earth-waves  are  comparable  with  one  another,  though 
produced  by  different  causes,  which  in  each  case 
bring  about  differential  movement  of  horizontal 
surfaces  in  contact  with  one  another.  One  layer  of 
air  moving  over  another  throws  the  lower  one  into 
waves,  which  are  often  defined  by  the  condensed 
aqueous  vapour  in  the  lower  layer ;  air  moving  over 
water  similarly  throws  the  water  into  waves ;  and, 
lastly,  differential  movement  of  different  layers  of 
the  earth's  crust  causes  the  rocks  to  be  thrown  into 
waves,  which  are  often  defined  by  the  superficial 
contour  of  the  ground,  as  well  as  by  the  folding  of 
the  planes  of  stratification.  The  identity  of  ap- 
pearance of  these  waves  is  illustrated  by  the  plate 
showing  clouds  in  the  Eden  Valley,  and  Fig.  3 
showing  earth-waves  in  the  Jura.  The  plate  shows 


22     SCIENTIFIC   STUDY   OF  SCENERY 

the  upper  surface  of  a  fog,  with  waves  produced 
by  a  light  breeze.  It  was  taken  on  a  calm  day 
in  January,  by  Mr.  E.  J.  Garwood,  from  the  slopes 
of  the  Crossfell  range,  overlooking  the  Eden  Valley 
in  Westmorland.  Fig.  3,  reproduced  from  The 
Limestone  Alps  of  Savoy,  by  kind  permission  of 
the  author,  Mr.  W.  G.  Collingwood,  is  a  bird's-eye 
view  of  part  of  the  Jura  mountains  and  the  Alps  of 
Savoy,  near  Geneva,  and  admirably  illustrates  the 
wave-like  character  of  these  mountain  ranges.  The 
similarity  between  the  cloud-waves,  earth-waves,  and 
ordinary  water-waves  is  rendered  perfectly  clear  by 
these  illustrations.  Dome  -  structure  may  be  pro- 
duced in  fluid  as  well  as  in  solid  media — witness  the 
cumulus  cloud,  the  geyser,  and  the  laccolite — but  the 
wave-structure  is  sufficient  for  purposes  of  illustration. 
As  the  result  of  this  change  the  flat  surfaces  produced 
by  accumulation  are  converted  into  surfaces  present- 
ing alternate  convex  ridges  and  concave  hollows. 

Further  diversity  is  produced  by  the  agents  of 
sculpture.  We  need  only  mention  in  passing  the 
effects  of  these  agents  upon  air  and  water-waves,  but 
must  devote  some  consideration  to  the  changes  which 
are  brought  about  by  them  upon  the  earth-waves. 

The  undulating  clouds  produced  owing  to  differ- 
ential movements  are  sculptured  by  winds  and  by 
differences  of  temperature.  The  wind  breaks  the 
masses  of  condensed  vapour  into  fantastic  forms, 
and  a  somewhat  similar  result  is  produced  by  the 
evaporation  of  a  fragment  of  cloud  here  and  the 
condensation  of  a  portion  of  vapour  there.  The 
ocean  waves  are  broken  up  by  wind,  ultimately 
producing  the  storm-wrack  and  spin  -  drift  of  the 
tempest-tossed  sea. 


PRODUCTION  OF  DOMINANT  FORMS     23 


24    SCIENTIFIC   STUDY   OF   SCENERY 

Similarly  the  earth-waves  are  carved  out  by  the 
graving-tools  of  nature,  and  the  effects  are  generally 
similar  to  those  produced  on  ocean-waves  by  the 
wind.  Indeed,  all  writers  upon  mountain  scenery 
have  been  led  to  compare  the  serried  ranks  of  hills 
with  the  broken  billows  of  a  stormy  sea.  Let  me 
quote  an  instance :  "  Suppose  the  sea  waves  exalted 
to  nearly  a  thousand  times  their  normal  height,  crest 
them  with  foam,  and  fancy  yourself  upon  the  most 
commanding  crest,  with  the  sunlight  from  a  deep 
blue  heaven  illuminating  such  a  scene,  and  you  will 
have  some  idea  of  the  form  under  which  the  Alps 
present  themselves  from  the  summit  of  the  Weiss- 
horn.  East,  west,  north,  and  south,  rose  those 
'  billows  of  a  granite  sea,'  back  to  the  distant  heaven, 
which  they  hacked  into  an  indented  shore."1 

The  scenery  of  the  earth's  crust  is  mainly  depend- 
ent upon  three  things,  namely,  the  structure  of  the 
crust,  the  nature  of  the  sculpturing  agent  or  agents, 
and  the  character  of  the  climate.  The  processes  of 
sculpture  are  known  to  geologists  by  the  name  of 
denudation.  Denudation  is  the  stripping  of  por- 
tions of  rock  from  one  place  and  their  removal 
to  another,  and  is  performed  by  agents  which  are 
generally  familiar  to  all.  Among  these  agents  may 
be  mentioned  change  of  temperature,  wind,  rain,  frost, 
rivers,  sea  waves,  and  action  of  organisms,  for  the 
most  part  assisted  by  gravitation,  as  the  result  of 
which  the  material  is  carried  from  a  higher  to  a 
lower  level,  and  ultimately  to  the  sea,  if  not  checked. 
Thus  the  land  is  the  great  theatre  of  destruction  by 
denuding  agencies,  and  the  ocean  the  great  re- 
ceptacle of  the  sediment  produced  by  these  agencies. 

1  TYNDALL,  Mountaineering  in  1861,  chap.  vi. 


i 


PRODUCTION  OF  DOMINANT  FORMS    25 

el  us  take  our  stand  at  the  foot  of  some  mountain 
cliff  on  a  winter  day.  The  stillness  of  the  frosty  air 
is  ever  and  anon  broken  by  the  fall  of  a  fragment 
of  rock  from  the  cliff  on  to  the  slope  beneath. 
This  fragment  has  commenced  its  journey  seaward. 
The  spring  freshet,  generated  by  the  melting  of  the 
snow,  may  wash  one  fragment  into  the  mountain 
burn,  there  to  be  dashed  against  many  a  similar 
fragment,  knocking  off  its  asperities,  and  rounding 
it,  while  the  broken  portions  are  worn  into  particles 
of  sand  and  dust.  If  we  take  up  a  position  on  some 
bridge  in  the  lower  reaches  of  the  river  during  a 
heavy  flood,  we  shall  find  the  swollen  waters  turbid 
with  the  sediment  produced  by  the  breakage  of  the 
rocks  above,  and  following  the  river  still  further  to 
its  junction  with  the  ocean,  may  notice  the  sand  banks 
and  mud  flats  accumulating  by  the  deposition  of  the 
sediment  where  the  current  of  the  river  is  checked 
upon  entering  the  sea.  Our  rock  -  fragment  and 
many  another  have  now  found  rest  until  disturbed 
by  other  changes.  If  we  travel  far  from  our  own 
country  to  the  arid  deserts  of  sub-tropical  regions  or 
the  ice-bound  hills  of  the  arctic  tracts,  we  shall  notice 
that  the  agents  are  in  some  ways  different,  but  the 
ultimate  effects  the  same.  The  materials  composing 
the  crust  are  constantly  being  broken  up,  and  carried 
from  a  higher  to  a  lower  level,  where  they  are  spread 
out  to  form  fresh  deposits.  The  agents,  I  say,  are 
in  some  ways  different,  and  here  the  effects  of  climate 
are  noticed.  Nature  works  in  the  wet  way  and  in 
the  dry  way,  to  borrow  an  expression  from  the 
chemist,  and  where  she  carries  out  the  processes  of 
denudation  in  the  wet  way,  in  regions  subjected  to 
considerable  rainfall,  the  scenic  results  differ  in  kind 


26     SCIENTIFIC   STUDY   OF   SCENERY 

from  those  characteristic  of  deserts  and  arctic  lands, 
where  much  of  the  work  is  performed  in  the  dry 
way. 

The  agents  of  denudation  are  at  work  over  all 
parts  of  the  earth's  surface  above  sea  level,  though 
their  effects  are  more  marked  in  some  places  than  in 
others.  In  one  place  rain  is  the  principal  agent,  in 
another  frost,  in  a  third  the  brook  or  river,  and 
accordingly  one  part  of  the  surface  is  more  worn 
than  another,  and  the  monotony  of  the  wave-curve 
is  broken  by  the  removal  of  less  material  from  one 
place  than  from  an  adjoining  one.  But  the  difference 
between  the  aspect  of  two  places  is  further  empha- 
sised by  the  difference  of  structure.  One  rock  is 
more  durable  than  another,  and  resists  the  work  of 
denudation  to  a  greater  extent.  Some  rocks  are 
harder  than  others,  and  tend  to  stand  out  after 
denudation  has  been  in  operation  for  some  time. 
Some  are  soluble,  others  practically  insoluble,  and 
in  this  case  the  insoluble  rock  will  tend  to  form 
eminences,  the  soluble  depressions.  One  rock  may 
be  separated  into  numerous  blocks  by  planes  of 
lamination,  joints,  and  cleavage-planes,  another  may 
possess  fewer  divisional  planes,  and  the  former  will  be 
more  easily  worn  away  than  the  latter. 

Again,  though  some  agent  of  denudation  is  at 
work  on  all  parts  of  the  earth's  surface,  the  amount 
of  material  which  accumulates  may  be  greater  than 
that  which  is  removed,  and  the  character  of  the 
surface  on  which  accumulation  takes  place  will  differ 
according  to  the  nature  of  the  accumulation.  The 
talus  slope  at  the  base  of  the  cliff,  the  alluvial  flat  by 
the  riverside,  the  sand  -  dune  on  the  sea-shore,  the 
cone  of  the  volcanic  vent,  are  caused  by  excess  of 


PRODUCTION  OF  DOMINANT  FORMS   27 

accumulation  over  material  removed  by  denudation. 
Each  has  its  own  character,  and  tends  to  diversify 
the  earth's  surface. 

We  shall  further  find  that  differential  movements  of 
portions  of  the  earth's  surface  produce  their  effects 
upon  scenery  over  and  above  the  development  of 
the  earth  -  waves.  The  earthquake  shock  tilts  up 
parts  of  the  earth  and  depresses  others,  producing 
fault-cliffs,  landslips,  and  often  damming  back  the 
waters  of  rivers,  causing  lakes.  A  similar  ponding 
back  of  waters  is  produced  by  slower  movements, 
which  occur  so  gradually  that  we  are  not  aware  of 
them  except  by  their  effects. 

As  the  results  of  accumulation  here,  of  denudation 
there,  of  difference  of  climate  in  different  places,  of 
difference  of  rock -structure,  of  variations  in  the 
nature  and  energy  of  the  denuding  agents,  of 
differences  in  the  nature  and  amount  of  the  materials 
which  are  accumulated,  and,  lastly,  of  the  operation 
of  earth-movements,  we  are  presented  with  those 
diversified  features  of  our  earth's  surface  which  it  is 
our  present  object  to  study  in  detail.  Here  we  meet 
with  mountain  chains,  there  with  rivers  meandering 
through  their  valleys ;  in  one  place  is  the  desert- 
floor,  in  another  the  fenland  flat.  Anon  we  stand 
by  the  sparkling  mountain  tarn ;  again  we  wander 
along  the  salty  borders  of  the  inland  sea.  At  one 
portion  of  the  river  -  course  we  find  the  stream 
foaming  amid  boulders,  or  hurled  boldly  over  the 
precipice,  at  another  winding  sluggishly  through 
oozy  swamps.  At  one  time  we  may  be  standing 
above  the  seething  cauldron  of  the  volcanic  vent,  at 
another  watching  the  apparently  motionless  sweep 
of  the  glacier.  The  eye  may  be  gladdened  by  the 


28     SCIENTIFIC   STUDY   OF   SCENERY 

vivid  carpet  of  Alpine  flowers  or  saddened  by  the 
monotonous  hue  of  the  desert  scrub.  We  may  gaze 
at  the  vivid  colouring  of  the  striped  rocks  of  the 
American  gorge  or  the  white  glint  of  the  chalk  cliffs 
of  Albion,  at  the  turbid  waters  of  the  Yellow  Sea  or 
the  azure  hue  of  the  Alpine  tarn.  Over  all  is  the 
ever-changing  sky,  with  the  clouds  hurrying  past, 
driven  by  the  tempest,  or  wreathing  languidly  around 
the  mountain-peak.  Happy  is  the  man  who  takes 
heed  of  these  things,  and  pleasurable  are  the 
emotions  which  are  excited  by  inquiry  into  the 
causes  which  have  produced  them  !  And  lives  there 
one  who,  communing  thus  with  Nature,  and  admitted 
to  some  of  her  secrets,  is  not  led  to  ponder  with 
reverence  upon  the  First  Great  Cause? 


CHAPTER    IV. 

THE    ATMOSPHERE 

THE  atmosphere  is  a  gaseous  envelope,  consisting 
of  a  mechanical  mixture  of  various  substances 
surrounding  the  lithosphere  and  hydrosphere,  and 
extending  outwards  to  an  unknown  distance  (pro- 
bably not  less  than  200  miles)  from  the  surface  of 
the  lithosphere.  As  is  well  known,  it  consists 
essentially  of  a  mixture  of  about  seventy-nine  parts 
of  nitrogen  and  twenty-one  of  oxygen ;  of  these 
oxygen  is  by  far  the  more  important  constituent ; 
of  the  other  components  which  are  important  with 
reference  to  our  present  inquiries  may  be  mentioned 
aqueous  vapour  and  carbon  dioxide  (carbonic  acid 
gas),  while  the  solid  particles  which  are  derived 
from  the  lithosphere  and  float  in  the  air  are  also 
of  importance. 

Colours  in  the  Sky. — The  prevalent  blue  colour  in 
the  clear  sky  is  produced  in  a  way  which  is  still  a 
topic  for  discussion  among  physicists,  and  it  would 
require  a  fuller  acquaintance  with  physical  principles 
than  can  be  assumed  here  in  order  to  present  the 
reader  with  an  intelligible  idea  of  the  suggestions 
which  have  been  made  to  account  for  this  blue 
colour.  Lord  Rayleigh  many  years  ago  suggested 
that  the  colour  was  due  to  the  occurrence  of  solid 
29 


3o     SCIENTIFIC   STUDY   OF  SCENERY 

particles  in  the  air.  It  is  generally  known  that  a 
ray  of  white  light  when  passed  through  a  prism  is 
broken  up  into  a  number  of  coloured  rays,  the  solar 
spectrum,  varying  from  violet  to  red.  The  length  of 
the  waves  of  different  coloured  light  varies,  the 
waves  of  the  red  light  being  longest,  those  of  the 
violet  shortest.  Now,  just  as  a  post  standing  in 
the  water  will  stop  and  reflect  the  small  waves  and 
let  the  larger  ones  pass  by,  so  the  short  waves  may 
be  stopped  by  particles  which  allow  the  larger  ones 
to  pass,  and  the  short  ones  are  reflected  to  the 
observer,  and  are  visible  to  him  as  blue ;  as  a  result 
of  this  the  sky  appears  blue.  Recent  experiments 
by  Professor  Dewar,  however,  show  that  the  colour 
of  pure  oxygen  is  blue,  and  the  colour  of  the  air  may 
be  simply  that  of  one  of  its  most  important  con- 
stituents. 

Whatever  be  the  cause  of  the  blue  colour,  the 
yellow  and  red  colours  seen  at  sunset  are  generally 
recognised  as  due  to  the  obstruction  of  the  rays  of 
small  wave-length.  In  this  case  the  colour  seen  is 
due  to  transmitted,  and  not  to  reflected,  light ;  hence 
it  is  the  rays  of  greater  wave-length,  which  are  not 
obstructed  by  the  particles,  which  appear  to  the 
observer.  As  the  obstructing  particles  are  found  in 
greater  abundance  in  the  lower  strata  of  the  at- 
mosphere, the  effect  of  the  obstruction  is  emphasised 
as  the  sun  sinks  lower,  and  the  violet  and  blue 
colours  are  replaced  by  yellow  and  orange,  and 
finally  by  red.1 

1  The  rose-coloured  glow  seen  on  the  higher  Alps  when  the  sun 
is  below  the  horizon  depends  partly  upon  the  above  conditions,  which 
are  further  complicated.  The  reader  will  find  an  explanation  of  the 
rosy  glow  given  by  Mr.  J.  Ball  in  a  note  appended  to  chap.  vii. 
of  Peaks,  Passes,  and  Glaciers. 


THE   ATMOSPHERE  31 

Any  occurrence  which  causes  the  existence  of  an 
abnormal  number  of  the  obstructing  particles  in  the 
atmosphere  will  intensify  the  character  of  the  sunset 
colours.  Readers  will  recollect  the  remarkable  sun- 
set glows  which  were  visible  in  our  country  as  well 
as  in  others  during  the  winter  and  spring  following 
the  violent  outbreak  of  the  volcanoes  of  Krakatoa 
in  1883.  There  is  evidence  that  the  wave  of  air 
produced  by  the  eruption  travelled  more  than  three 
times  round  the  earth,  and  that  fine  dust  from  the 
volcano  was  carried  with  it,  and  there  is  good  reason 
for  supposing  that  the  vivid  sunset  effects  referred  to 
above  were  produced  as  the  result  of  the  existence 
of  this  dust  in  the  atmosphere.1 

Nature  and  Forms  of  Clouds. — The  importance  of 
the  presence  of  aqueous  vapour  in  the  atmosphere 
has  already  been  noted.  Different  portions  of  the 
atmosphere  contain  varying  proportions  of  aqueous 
vapour,  the  usual  proportion  being  about  1*5  per 
cent.,  and  this  when  condensed  forms  cloud.  It  is 
evident  that  the  atmosphere  cannot  contain  an  un- 
limited quantity  of  the  vapour,  and  when  it  holds 
as  much  as  it  can  carry  without  any  portion  being 
condensed  it  is  said  to  be  saturated. 

It  is  also  known  that  air  when  at  a  high  tempera- 
ture can  hold  more  vapour  than  when  at  a  lower 
one ;  hence  condensation  does  not  always  take  place 
at  the  same  temperature :  in  other  words,  the  dew- 
point,  or  temperature  at  which  condensation  occurs, 
varies  with  the  amount  of  aqueous  vapour  in  the 
air.  The  condensation  of  the  vapour  gives  rise  to 
numerous  droplets  of  water  which  compose  clouds ; 

1  See  Royal  Society  Report  on  Krakatoa^  1888. 


32     SCIENTIFIC   STUDY   OF   SCENERY 

these  when  at  a  low  level  are  termed  fogs  or 
mists.1 

There  are  various  ways  in  which  the  chilling  of 
the  atmosphere,  which  brings  about  condensation, 
may  be  effected,  as  (i)  radiation;  (ii)  ascent  of 
moisture-laden  air  into  higher  and  therefore  colder 
regions  of  the  atmosphere ;  (iii)  contact  of  moisture- 
laden  air  with  a  cold  body  as  the  solid  ground ;  and 
(iv)  admixture  of  masses  of  cold  and  hot  air. 

"the  form  of  clouds  depends  to  a  large  extent  upon 
movements  of  the  atmosphere,  which  are  in  turn  due 
to  differences  of  barometric  pressure.  The  way  in 
which  these  movements  are  set  up  will  be  referred 
to  anon.  But  though  winds  produce  marked  effects 
upon  the  clouds,  their  primary  shape  depends  upon 
movements  which  take  place  so  slowly  that  they 
would  hardly  be  termed  winds,  and  these  movements 
take  place  vertically  as  well  as  horizontally,  the 
shapes  of  some  clouds  being  largely  due  to  vertical 
movements,  those  of  others  to  movements  in  a  hori- 
zontal direction,  while  others  again  are  produced  by 
a  combination  of  the  two  sets  of  movements. 

Clouds  may  be  classified  according  to  their  shapes, 
or  according  to  their  modes  of  origin,  but  as  the 
former  is  largely  dependent  upon  the  latter,  the  two 
classifications  are  similar.  Nevertheless,  there  is  still 
much  diversity  of  opinion  as  to  the  classification  to 
be  adopted.  Clouds  were  originally  classified  by  Mr. 
L.  Howard  in  i8o3.2  He  defined  three  primary  types 

1  Mr.   J.   AITKEN  (Trans.    Roy.  Soc.,  Edin.,   vol.   xxx.,   p.    337) 
maintains  that  the  presence  of  foreign  bodies  as  particles  of  dust  in 
the  atmosphere  is  necessary  to  the  production  of  condensation.     This 
necessity  has  been  questioned. 

2  HOWARD,  L.,  Essay  on  the  Modifications  of  Clouds. 


THE   ATMOSPHERE  33 

of  cloud,  namely  cirrus,  cumulus,  and  stratus,  and 
four  compound  types  formed  by  combinations  of 
these  :  cirro-cumulus,  cirro-stratus,  cumulo-stratus ,  and 
nimbus  ;  the  last  is  a  term  applied  to  any  cloud  from 
which  rain  is  falling,  and  can  hardly  be  included 
among  the  other  types,  and  accordingly  we  are  left 
with  three  primary  and  three  secondary  types.1 

According  to  their  origin,  Mr.  Clement  Ley  classifies 
clouds  as  clouds  of  radiation,  including  some  kinds  of 
fog,  clouds  of  inversion,  as  cumulus,  clouds  of  interfret, 
as  stratus,  and  clouds  of  inclination,  as  cirrus,  and  it 
will  be  most  convenient  to  adopt  this  classification 
when  considering  the  principal  types  of  cloud. 

(i)  Clouds  of  Radiation. — The  ground  becomes 
cooled  by  radiation  of  heat  into  space,  and  when 
cooled  below  dew-point  the  air  in  immediate  contact 
with  the  ground  deposits  its  moisture  as  dew,  but 
the  air  above  this,  containing  solid  particles,  is  also 
chilled,  and  the  solid  particles  themselves  become 
cooled  by  radiation.  Accordingly  moisture  is  de- 
posited on  the  solid  particles,  giving  rise  to  one 
form  of  fog.  This  may  be  complicated  when  low 
ground  is  surrounded  by  higher  ground  by  inter- 
mixture of  cold,  vapour-charged  air  from  the  higher 
ground  with  that  which  immediately  overlies  the  low 
country.  The  fog  whose  upper  surface  is  seen  in 
the  plate  showing  clouds  in  the  Eden  Valley  was  of 
this  composite  character.  Fogs  due  to  radiation  have 

1  The  reader  will  find  an  account  of  cloud-shapes  and  cloud-forma- 
tion in  Elementary  Meteorology,  by  R.  H.  SCOTT,  F. R. S.  (International 
Scientific  Series) ;  in  Cloudland,  by  the  Rev.  W.  CLEMENT  LEY 
(Stanford,  1894) ;  and  in  a  paper  by  A.  F.  OSLER,  "On  the  Normal 
Forms  of  Clouds,"  Report  of  the  British  Association  for  1886  (Bir- 
mingham), p.  530.  From  these  works  the  account  of  clouds  given  here 
is  largely  taken. 
D 


34     SCIENTIFIC   STUDY   OF   SCENERY 

been  termed  "radiation  fogs"  by  Herschel,  to  dis- 
tinguish them  from  other  fogs,  which  present  affinities 
to  other  classes  of  cloud,  for  "  clouds  ...  are  really 
nothing  else  but  fog  or  mist,  and  the  most  solid- 
looking  night-cap  on  a  hill-top  is  found  by  those 
who  are  enveloped  in  it  to  be  neither  more  nor  less 
than  a  driving  mist."1 

(ii)  Clouds  of  Inversion. — These  clouds  are  due  to 
an  upward  movement  of  a  portion  of  the  atmo- 
sphere, which  tends  to  produce  interchange  of  air 
between  lower  and  higher  atmospheric  strata.  The 
upward  movement  is  due  to  a  mass  of  air  in  a  lower 
stratum  being  rendered  lighter  than  it  was  previously, 
either  owing  to  its  becoming  charged  with  vapour, 
thus  diminishing  its  specific  gravity,  or  on  account  of 
its  expansion  when  heated  by  the  rays  of  the  sun. 
As  the  rising  column  of  air  reaches  higher  altitudes, 
it  becomes  chilled,  and  some  of  the  vapour  is  con- 
densed, forming  cloud,  the  base  of  which  may  be 
level.  The  process  of  condensation  liberates  heat, 
which  causes  further  rise  and  condensation,  until  the 
upper  part  of  the  column  becomes  chilled  below 
the  temperature  of  the  surrounding  air,  and  a  down- 
ward movement  takes  place  at  the  top.  In  this  way, 
speaking  briefly,  are  formed  cumulus  clouds,  which 
have  not  inaptly  been  compared  by  Tyndall  to  the 
steam  escaping  from  the  funnel  of  a  locomotive.  The 
friction  of  the  particles  of  the  minute  droplets  is 
sufficient  to  prevent  them  from  falling  *vhen  raised 
to  the  required  height.2  These  cumulus  clouds  are, 
in  our  country,  essentially  clouds  of  summer,  and 
also  clouds  of  the  day-time. 

1  SCOTT,  R.  H.  op.  «?.,  p.  123. 

*  For  further  account  of  formation  of  cumulus,  see  LEY,  Cloudland, 
chap,  i.  and  Fig.  I. 


THE   ATMOSPHERE  35 

(iii)  Clouds  of  Inter/ret  are  due  to  the  existence 
of  two  successive  strata  of  afr  moving  in  different 
directions,  or  moving  in  the  same  direction,  but  with 
different  velocities.  A  certain  amount  of  intermixture 
will  take  place  about  the  plane  of  junction,  and  if 
condensation  occur,  straight  sheets  of  cloud — stratus 
— will  be  formed.  As  has  already  been  seen,  a  series 
of  waves  will  be  developed  on  the  bounding  plane, 
as  the  result  of  movement,  which  may  give  rise  to 
various  complications.  If  the  upper  stratum,  as  is 
usually  the  case,  is  the  colder,  the  wave-crests  of  the 
lower  stratum  will  be  at  a  higher  level  than  the  troughs, 
and  therefore  the  air  of  the  wave-crests  colder  than 
the  air  of  the  troughs.  Accordingly  condensation  may 
occur  on  the  wave-crests,  and  not  in  the  troughs,  thus 
giving  rise  to  detached  clouds,  which,  if  the  waves 
are  linear,  will  run  in  parallel  lines,  while,  if  the  waves 
are  complicated,  the  clouds  may  be  "cut  up  into  small 
waves,  ripples,  and  vortices  like  a  '  choppy  sea.'  In 
this  .  .  .  case  we  have  innumerable  patches  and 
flecks  of  cloud  so  often  seen  in  fairly  quiet  weather 
in  summer."1  The  wavy  surface  of  the  fog  seen  in 
the  plate  showing  the  upper  surface  of  cloud  in  the 
Eden  Valley  is  due  to  the  movement  of  an  upper 
stratum  over  a  lower  one,  the  latter  in  this  case 
being  the  cooler,  but  here  the  waves  are  due  to 
mechanical  disturbance  of  air  in  which  the  vapour 
has  already  been  condensed.  Condensation  in  the 
crests  of  complex  waves  is  undoubtedly  the  cause 
of  one  form  of  the  cloud-group  which  is  somewhat 
loosely  spoken  of  as  "  mackerel  -  sky,"  and  this 
particular  form  is  termed  stratus  maculosus  by 
Mr.  Ley,  though  some  writers  upon  clouds  have 
1  LEY,  C.,  op.  at.,  p.  13. 


36     SCIENTIFIC   STUDY   OF   SCENERY 

called  the  mackerel -sky  cirro-cumulus.  There  is, 
however,  another  way  in  which  a  stratiform  mass 
of  vapour  may  be  cut  up  into  detached  por- 
tions, as  described  by  Mr.  Osier,  by  a  combina- 
tion of  lateral  and  vertical  movements.  Suppose 
that  a  sheet  of  stratus  -  cloud,  produced  by 
differential  horizontal  movement  of  adjacent  strata, 
is  bodily  elevated -as  a  result  of  vertical  movement, 
greatest  at  one  point,  and  dying  out  laterally;  the 
original  flat  mass  will  take  a  gentle  curved  form,  and 
will  therefore  occupy  more  superficial  area  than 
before,  and  the  cloud  will  be  ruptured  in  the  same 
way  as  a  pane  of  glass  when  struck  by  a  stone. 
As  Mr.  Osier  remarks,  it  "  will  be  rent  into  frag- 
ments or  small  groups,  and  thus  produce  what  is 
called  a  '  mackerel-sky,'  just  as  a  similar  result  is 
produced,  but  by  the  reverse  action,  in  mud  that 
has  dried  up  and  shrunk  into  small  patches  while 
the  damp  earth  beneath  remains  expanded  by  the 
moisture  it  still  contains." 

As  the  result  of  vertical  movement  followed  by 
horizontal  movement,  cumulus  cloud,  as  noted  by 
Mr.  Osier,  may  be  converted  into  a  stratiform  cloud, 
cumulo-stratus.  "  The  friction  of  the  earth  from  the 
irregularities  of  its  surface,  and  the  denser  state  of 
the  lower  air,  causing  it  to  flow  less  rapidly  than 
that  which  is  higher  and  more  attenuated,  the  upper 
portion  of  a  cloud  moves  more  rapidly  than  the 
lower,  and  the  cumulus  shears  over  into  a  slanting 
position,  and  finally  assumes  the  form  of  the  cumulo- 
stratus,  and,  however  reduced  in  depth  or  thickness 
the  cloud  may  become  by  this  flattening  and  some- 
what attenuating  process,  the  cumulus  character, 
though  much  diminished,  is  seldom,  if  ever,  entirely 


THE   ATMOSPHERE  37 

obliterated."  The  writer  aptly  illustrates  this  by 
reference  to  the  flat  brown  cloud  of  smoke  from  a 
passing  steamer,  which  came  from  the  funnel  in 
great  rounded  masses.  We  may  sometimes  observe 
one  set  of  clouds  having  a  linear  arrangement  per- 
pendicular to  the  direction  in  which  the  wind  is 
blowing,  while  another  set  has  a  linear  arrangement 
parallel  to  this  direction.  When  the  wind  is  slight, 
cloud  waves  are  developed  at  right  angles  to  the 
direction  in  which  the  wind  is  blowing.  With  a 
strong  wind,  we  often  notice  bars  of  stratiform  cloud 
running  parallel  to  the  wind's  direction,  and  if  the 
wind  be  strong  near  the  earth's  surface  and  gentler 
above,  two  sets  of  stratiform  clouds  may  occur  at 
the  same  time,  the  upper  with  lines  at  right  angles 
to  the  wind's  direction  and  the  lower  arranged  in 
lines  parallel  to  it. 

The  cloud-banner,  which  is  often  observed  on  the 
lee-side  of  a  mountain,  is  a  particular  form  of  stratus, 
condensation  only  taking  place  in  the  upper,  faster- 
moving  stratum  when  it  is  chilled  below  dew-point 
by  contact  with  the  cold  surface  of  the  mountain. 
As  is  well  known,  though  the  cloud  is  often  stationary, 
it  is  constantly  changing  its  substance,  fresh  vapour 
being  condensed  against  the  mountain  as  the  pre- 
viously condensed  vapour  becomes  evaporated  some 
distance  on  the  lee-side  of  the  mountain. 

(iv)  Clouds  of  Inclination. — The  principal  clouds  of 
inclination  are  cirrus,  which  are  formed  high  above 
the  earth's  surface.  In  the  rarefied  atmosphere  at 
these  heights,  when  water  vapour  is  condensed  into 
cloud,  it  can  fall,  owing  to  its  weight,  to  lower  parts 
of  the  atmosphere,  and  if  these  are  moving  more 
slowly  than  the  upper  layers,  as  will  probably  be  the 


38     SCIENTIFIC   STUDY   OF   SCENERY 

case,  the  upper  part  of  the  cloud  moves  faster  than 
the  lower,  which  lags  behind,  thus  giving  rise  to  the 
characteristic  curved  form  of  the  cirrus  or  curl-cloud. 
As  the  condensed  vapour  falls  still  lower  it  gets  to 
a  stratum  in  which  the  air  is  sufficiently  warm  to 
allow  of  the  re-evaporation  of  the  condensed  matter, 
and  thus  the  cloud  probably  ends  in  a  point.  It  is 
known,  from  observation  of  the  characters  of  haloes 
and  mock-suns,  that  these  elevated  clouds  of  inclina- 
tion are  often  formed  of  spicules  of  ice,  and  not  of 
drops  of  water. 

There  is  general  agreement  as  to  the  mode  of 
origin  of  the  primary  types  of  clouds,  but  enough  has 
been  said  to  show  that  the  various  processes  which 
form  and  shape  the  clouds  may  act  in  combination, 
and  when  we  add  to  this  the  modifications  which 
are  produced  by  winds,  changes  of  temperature,  and 
other  minor  causes,  after  the  clouds  have  once  been 
formed,  we  need  not  be  astonished  at  the  infinite 
variety  presented  by  cloud  outlines,  which,  while 
rendering  the  sky  a  subject  for  profound  contempla- 
tion and  reverence  by  the  lover  of  scenery,  causes 
the  student  of  cloud -classification  to  experience  a 
feeling  of  bewilderment  when  he  is  confronted  with 
the  great  differences  in  the  nomenclature  adopted 
by  different  writers  in  their  treatment  of  secondary 
and  complex  cloud-types. 

Distribution  of  Clouds. — It  has  already  been  noted 
that  certain  clouds  occur  at  some  times  and  seasons 
more  than  at  others ;  in  other  words,  clouds  have  a 
diurnal  as  well  as  an  annual  distribution  ;  but,  besides 
this  distribution  in  time,  we  have  a  distribution  in 
space,  both  horizontal  and  vertical.  With  regard  to 
the  vertical  distribution,  it  is  easily  seen  that  clouds 


THE    ATMOSPHERE  39 

of  different  types  do  not  exist  at  the  same  height ; 
many  of  us  have  been  in  or  above  stratus  or  even 
secondary  types  of  cumulus,  and  still  found  cirrus  far 
above  us.  The  following  may  be  taken  as  the  average 
heights  for  the  primary  types  of  cloud  : — 

Stratus  .         .       3000  to  20,000  feet. 

Cumulus  .         .       4000  to  10,000    ,, 

Cirrus  .         .    25,000  to  30,000    ,, 

The  horizontal  distribution  of  different  kinds  of 
clouds  in  space  is  affected  by  the  time-variations, 
but  over  and  above  this  it  is  specially  affected  by 
types  of  weather,  and  the  connection  of  different 
types  of  clouds  with  weather  variations  is  a  matter 
of  such  great  importance  to  us  that  it  is  remarkable 
how  little  interest  is  evinced  in  it  by  the  majority  of 
people.  The  local  shepherd  "  can  discern  the  face 
of  the  sky"  and  foretell  the  weather  with  considerable 
accuracy  as  the  result  of  close  observation  of  the 
changes  in  the  heavens,  but  comparatively  few 
people  are  weatherwise  owing  to  their  knowledge 
of  these  changes,  and  most  of  us  base  our 
prognostications  on  the  changes  of  the  barometer, 
and  are  apt  to  speak  lightly  of  the  weather 
reports  in  our  daily  papers,  though  these  are 
drawn  up  as  the  result  of  barometric  observations 
over  wide  areas  in  addition  to  numerous  observations 
on  the  character  of  the  sky  in  these  areas.  We  read 
that  "  a  cyclone  is  approaching  our  shores,"  and  if 
we  give  more  thought  to  it,  we  are  probably  satisfied 
with  a  further  statement  that  "  showery  weather  may 
be  experienced  in  our  northern  and  north-western 
counties,"  and  may  give  no  heed  to  the  glorious 
changes  in  the  canopy  of  clouds  which  are  likely  to 


40     SCIENTIFIC   STUDY   OF   SCENERY 

accompany  the  passage  of  this  cyclone.  Let  us 
briefly  consider  the  probable  nature  of  these  changes. 
It  will  be  necessary  at  the  outset  to  say  something 
about  cyclones. 

The  atmosphere  is  heated  by  the  sun,  but  it  is 
transparent  to  the  direct  rays  of  the  sun,  and  receives 
its  heat  from  the  dark  rays  given  off  by  the  earth's 
surface.  Accordingly  the  lower  strata  of  the  earth 
become  most  heated,  and  the  temperature  falls  as 
one  passes  from  sea-level  to  higher  altitudes.  Now, 
heated  air  expands,  and  a  given  bulk  becomes  lighter 
when  heated,  on  account  of  this  expansion,  and  also 
because  hot  air  can  hold  more  water  vapour  than 
cold,  and  the  water  vapour  is  lighter  than  the  air 
which  it  displaces.  The  lighter  heated  air  tends  to 
rise,  and  accordingly,  if  one  spot  in  the  earth's  surface 
is  heated  more  than  the  surrounding  area,  the  air 
above  the  spot  rises,  and  the  column  of  air  above 
that  spot  is  higher  than  those  above  the  surrounding 
places,  and  the  top  of  this  elevated  column  will  flow 
out  at  the  top  of  the  atmosphere  in  order  to  restore 
equilibrium,  just  as  water  will  flow  from  one  vessel 
to  another  when  the  surface  of  the  water  is  at  a 
different  level  in  the  two  vessels  if  the  barrier 
between  them  be  removed.  Asa  result  of  this,  the 
columns  of  air  around  the  column  which  rose  owing 
to  expansion  will  contain  more  air  than  they  did 
originally,  and  these  columns  will  therefore  press 
on  the  earth's  surface  with  force  greater  than  that 
exerted  before  the  disturbance  of  equilibrium.  We 
have,  in  fact,  a  point  of  low  barometric  pressure, 
surrounded  by  a  ring  or  area  of  high  barometric 
pressure.  This  system  is  not  yet  in  equilibrium, 
and  equilibrium  is  restored  by  the  movement  of 


THE   ATMOSPHERE  41 

air  from  the  ring  of  high  pressure  to  the  point  of 
low  pressure  just  above  the  surface  of  the  earth. 
Air,  then,  tends  to  flow  upwards  and  outwards  in  the 
higher  regions  of  the  atmosphere  from  areas  of  low 
pressure  to  areas  of  high  pressure,  and  to  flow  down- 
wards and  inwards  in  the  strata  immediately  over- 
lying the  earth's  surface  from  areas  of  high  pressure 
to  areas  of  low  pressure.  It  is  the  latter  movements 
which  specially  concern  us. 

If  the  earth  were  stationary,  the  movements  would 
be  in  straight  lines,  but,  owing  to  the  earth's  rotation, 
the  movements  are  really  spiral.  The  earth  is 
rotating  on  its  axis  from  west  to  east,  and  the  air 
is  carried  round  with  it.  Thus  a  point  on  the  equator 
performs  a  journey  of  about  24,000  miles  per  diem, 
and  the  same  is  the  case  with  a  particle  of  air  just 
above  it,  while  a  point  at  the  poles  is  stationary,  and 
points  situated  between  pole  and  equator  perform 
a  longer  or  shorter  journey  according  to  their  near- 
ness to,  or  remoteness  from,  the  equator.  Now,  a 
particle  of  air  moving  in  a  northerly  or  southerly 
direction  retains  for  some  time  the  initial  velocity 
which  it  possessed  owing  to  the  movement  of  rotation. 
Suppose  a  particle  of  air  in  the  northern  hemisphere 
to  be  travelling  from  north  to  south  ;  it  proceeds  from 
a  place  with  relatively  small  velocity  to  one  with 
greater,  and  accordingly  appears  to  lag  behind,  and, 
instead  of  reaching  a  point  due  south  of  its  starting- 
point  will,  reach  one  south-westward  of  it.  Again,  a 
particle  in  the  same  hemisphere  travelling  from  south 
to  north  starts  with  considerable  velocity,  communi- 
cated by  the  earth's  rotation,  and  travels  to  a  point 
where  the  velocity  of  a  point  on  the  earth  is  less 
than  its  own  ;  so  it  appears  to  advance  instead  of 


42     SCIENTIFIC   STUDY   OF  SCENERY 

lagging  behind,  and,  instead  of  reaching  a  point  due 
north  of  its  starting-point,  will  reach  one  to  the  north- 
eastward. In  each  case  the  wind  is  deflected  to  the 
right  of  its  direct  course,  and  this  is  so  with  all  winds 
in  the  northern  hemisphere,  except  those  blowing 
due  east  or  due  west.  It  will  be  found  that  in  the 
southern  hemisphere  the  winds  are  similarly  deflected, 
but  to  the  left  of  their  direct  course.  In  the  case  of 
a  point  of  low  pressure  surrounded  by  a  ring  of  high 

7 


\ 
X 


A  B 

FIG.  4. 

A.  Cyclone.  X.   Low-pressure  point. 

B.  Anti-cyclone.     Y.   High-pressure  point. 

Arrows  show  direction  of  wind. 

pressure  area  the  winds  to  the  north  of  the  point  are 
deflected  westward,  those  to  the  south  of  it  eastward, 
and  air  does  not  flow  in  directly  to  the  point  of  low 
pressure  from  all  surrounding  points,  but  flows  in 
spirally  in  a  direction  contrary  to  the  direction  of 
movement  of  the  hands  of  a  watch  in  the  northern 
hemisphere.  Such  a  system  is  called  a  cyclone 
(Fig.  4  A). 

A  cyclone,  then,  is  a  system  of  winds  blowing  in 
spirally  downwards  towards  a  low  pressure  area 
from  a  surrounding  area  of  high  pressure,  and  the 


THE   ATMOSPHERE  43 

winds  move  in  a  direction  contrary  to  the  hands 
of  a  watch  in  the  northern  hemisphere,  and  in  the 
direction  of  the  hands  in  the  southern  hemisphere. 

Conversely  an  anti-cyclone  (Fig.  4  B}  is  a  system  of 
winds  blowing  spirally  upwards  to  a  high  pressure 
area  from  a  surrounding  area  of  low  pressure,  and  in 
this  case  the  winds  move  in  the  direction  of  the 
hands  of  a  watch  in  the  northern  hemisphere,  and 
in  the  contrary  direction  in  the  southern  hemisphere. 

The  velocity  of  the  winds  of  a  cyclonic  system  is 
generally  much  greater  than  that  of  the  winds  of  an 
anti-cyclonic  system,  and  accordingly  cyclones  are 
often  accompanied  by  gales  and  storms,  anti-cyclones 
by  calm. 

The  centre  of  a  wind  system  is  not  usually 
stationary  for  any  length  of  time,  but  has  itself  a 
more  or  less  definite  path,  which,  in  the  case  of  our 
islands,  is  usually  in  a  north-easterly  direction  along 
a  line  running  south-west  and  north-east ;  hence  we 
so  frequently  read  of  cyclones  approaching  our  shores 
from  the  Atlantic. 

The  shape  of  the  system  may  be  circular,  or  may 
be  elliptical.  In  the  latter  case,  when  the  longer 
axis  of  the  ellipse  is  a  considerable  multiple  of  the 
shorter  diameter,  only  one  side  of  the  ellipse  is  likely 
to  occur  over  our  islands  at  once ;  this  forms  a  figure 
in  the  shape  of  a  V,  and  accordingly  we  speak  of 
the  half  of  an  elongated  cyclone  as  a  V-shaped 
depression,  while  that  of  an  elongated  anti-cyclone 
is  known  as  a  col,  or  ridge  between  two  V-shaped 
depressions. 

Now  the  type  of  cloud  over  our  islands  and 
elsewhere  is  largely  dependent  upon  the  nature  of 
the  wind  system  which  affects  the  areas. 


44     SCIENTIFIC   STUDY   OF   SCENERY 

An  anti- cyclone  is  usually  marked  by  quiet 
weather ;  the  long  periods  of  dry  weather  in  summer, 
the  prolonged  fogs  of  autumn,  and  frosts  of  winter 
occur  during  the  prevalence  of  anti  -  cyclonic  con- 
ditions. Clear  skies  or  fogs  are  frequent  accom- 
paniments, or,  if  the  sky  be  cloudy,  we  find  a  haze 
and  belts  of  stratus,  with  cirrus  in  the  higher 
regions.  Anti-cyclonic  conditions  are  by  no  means 
always  conducive  to  fine  scenic  effects,  and  in 
mountain  regions  especially  the  hills  are  apt  to  be 
obscured  by  haze  for  days  together,  and  the  colour- 
ing is  frequently  monotonous. 

When  a  cyclone  passes,  there  is  often  a  definite 
relationship  between  the  different  portions  of  the 
cyclone  and  the  nature  of  the  cloud.  In  front  of 
an  advancing  cyclone,  gossamer-like  threads  of  the 
secondary  cloud  of  inclination  known  as  cirro-filum 
are  seen,  followed  by  a  thicker  mass  of  veil-like  cirro- 
velum.  This  is  followed  by  the  nimbus  or  complex 
mass  of  cloud,  from  which  rain  is  discharged.  The 
centre  of  the  cyclone  is  marked  by  alternate  patches 
of  blue  sky  and  broken  clouds.  In  the  rear  of  the 
cyclone  cumulus  is  abundant,  especially  on  the  south 
side  of  the  system,  with  stratus  on  the  north  side ; 
and,  lastly,  we  have  bands  of  cirrus  and  its  secondary, 
cirro-macula.1 

Thunderstorms  occur  when  an  area  is  occupied 
by  a  low-pressure  system,  though  the  system  is  not 
always  of  the  same  nature.  Most  of  our  summer 
thunderstorms  are  accompaniments  of  small,  shallow 
depressions  (that  is,  depressions  where  the  pressure 
in  the  centre  is  not  very  different  from  the  pressures 
around),  while  other  thunderstorms  occur  along  the 
1  See  diagram,  LEY,  C.,  Cloudland,  Plate  VI.,  facing  p.  176. 


THE    ATMOSPHERE  45 

edges  of  deep,  cyclonic  disturbances,  and  may  occur 
at  all  seasons.1 

1  Besides  electrical  phenomena,  there  are  various  optical  phenomena, 
as  rainbows,  mock -suns,  haloes,  which  are  of  interest  to  the  student  of 
scenery,  but,  on  account  of  their  comparative  rarity,  it  is  unnecessary 
to  treat  of  them  in  a  work  like  the  present.  The  reader  will  find  an 
account  of  them  in  Mr.  R.  H.  Scott's  Elementary  Meteorology, 
chaps,  x.  and  xi. 


CHAPTER   V. 

MAIN   FEATURES   OF  CONTINENTS  AND 
OCEAN   BASINS 

IT  is  generally  recognised  that  the  land  surfaces 
of  the  globe  are  essentially  areas  of  denudation 
or  destruction  of  rock,  and  the  ocean  basins,  regions  of 
reception  and  deposition  of  sediment,  in  other  words 
that  rock-strata  are  on  the  whole  manufactured  in 
the  oceans,  destroyed  on  the  dry  land.  The  oceanic 
origin  of  the  major  portion  of  the  strata  which  now 
form  our  land  surfaces  is  amply  proved  by  the 
general  occurrence  of  the  remains  of  marine  organisms 
within  them,  and  the  comparative  rarity  of  terrestrial 
or  fresh-water  organisms.  We  have  thus  indisput- 
able proofs  that  our  land  masses  have  not  always 
existed  as  dry  land,  but  that  large  tracts  of  them 
have  been  submerged  beneath  the  ocean  waters. 
Proofs  are  also  forthcoming,  though  they  are  naturally 
not  so  patent,  that  tracts  of  present  ocean-floor  once 
existed  as  dry  land,  but  as  the  student  of  scenery  is 
not  directly  concerned  with  the  aspect  of  the  ocean- 
floor,  it  is  unnecessary  to  enter  into  this  matter  at 
length. 

Admitting  that  extensive  tracts  of  dry  land  have 

been  submerged,  it  is  necessary  to  account  for  their 

emergence,   which   may   be   brought   about    in    two 

ways :  either  by  movement  of  the  water,  or  upheaval 

46 


CONTINENTS   AND   OCEAN    BASINS     47 

of  the  outer  part  of  the  lithosphere  above  water-level. 
Our  first  thought  would  naturally  be  that  the  level  of 
the  mobile  ocean  rather  than  that  of  the  apparently 
stable  earth -crust  would  be  changed  in  order  to 
produce  the  land  masses,  but  a  number  of  facts  prove 
that  it  is  the  land  which  has  risen  above  the  ocean 
level,  and  not  the  latter  which  has  changed.  Promi- 
nent among  these,  and  sufficient  for  our  purpose,  is 
the  fact  that  the  strata,  originally  laid  down  in 
horizontal  sheets,  are  now  found  inclined  at  various 
angles,  sometimes  vertical,  or  even  overturned,  and 
as  these  strata  compose  the  lithosphere,  the  statement 
that  the  strata  have  been  moved  is  the  same  as  the 
statement  that  the  lithosphere  has  been  moved.  The 
cause,  or  rather  causes,  of  this  movement  do  not 
directly  concern  us  in  our  present  inquiry,  and 
there  is  a  considerable  amount  of  uncertainty  on 
the  subject  in  the  minds  of  geologists,  though  the 
contraction  of  the  earth's  crust  is  generally  con- 
sidered to  be  the  most  important  factor  in  producing 
earth  movement.  The  earth  is  hotter  inside  than 
outside.  Now  a  cooling  body  contracts  more  when 
suffering  the  loss  of  a  given  amount  of  heat  if  it 
be  at  a  high  temperature  than  if  at  a  lower  one ; 
accordingly  the  hot  interior  of  the  earth  would 
contract  more  than  the  cooler  exterior,  and  tend  to 
shrink  away  from  it,  but  the  weight  of  the  exterior 
would  prevent  the  formation  of  a  space,  and  the 
exterior  would  settle  down  in  wrinkles,  just  as  an 
apple  wrinkles  owing  to  the  loss  of  more  moisture 
from  the  interior  than  from  the  rind.  Whether  this 
be  the  true  explanation  or  not,  inspection  of  the 
earth's  crust  shows  that  it  has  been  wrinkled  into 
a  wavy  surface,  very  like  the  surface  of  an  ocean 


48     SCIENTIFIC   STUDY   OF   SCENERY 

ruffled  by  the  wind.  In  places  we  find  evidence 
of  alternate  ridges  and  troughs ;  in  other  places, 
where  the  movements  have  been  complicated,  the 
earth  is  like  an  ocean  surface  affected  by  a  choppy 
sea,  two  or  more  sets  of  movements  having  occurred 
at  different  angles,  and  just  as  the  major  waves 
of  the  sea  are  often  accompanied  by  minor  ripples 
on  their  surfaces,  so  we  find  minor  folds  of  the 
earth's  crust  superposed  upon  the  larger  ones. 
Every  earth-wave  may  be  looked  upon  as  composed 
of  two  parts,  a  trough  and  an  arch,  with  a  septum 
common  to  the  two,  and  as  in  the  case  of  the  sea- 
wave,  so  with  the  earth-wave,  there  is  a  tendency  for 
the  slope  of  the  septum  to  be  steeper  than  that  of 
the  other  portions  of  the  wave,  as  shown  in  Fig.  5. 

In  this  case  the  wave  system  as  a  whole  has  moved 
in  the  direction  indicated  by  the  arrow.  Now  a 
movement  of  this  character,  if  on  a  sufficiently  large 
scale,  might  give  rise  to  an  ocean  basin  in  the  trough 
and  a  continental  uplift  on  the  arch,  assuming  that 
the  crust  had  previously  been  exactly  at  sea-level, 
and  we  may  briefly  inquire  if  there  is  any  evidence 
that  continents  and  ocean  basins  are  due  to  move- 
ments of  this  nature.1 

It  requires  little  study  of  geological  literature  to 
discover  that  as  a  general  rule  the  most  elevated 
parts  of  continental  masses  are  those  in  which  the 
strata  have  undergone  most  disturbance  in  compara- 
tively recent  geological  times ;  the  flat  tracts  of  Russia 
are  composed  of  horizontal  strata,  the  sloping 
plateaux  of  North  America  of  gently  inclined  strata, 

1  A  very  suggestive  account  of  the  structure  of  continents  and  ocean 
basins  will  be  found  in  Professor  Lapworth's  address  to  section  C  of 
the  British  Association,  Rep.  Brit.  Assoc.,  Edinburgh,  1892,  p.  695. 


CONTINENTS   AND   OCEAN    BASINS     49 

the  craggy  summits  of  the  Alpine  chains  of  highly 
contorted  rocks,  and  further  study  shows  that  if 
we  omit  the  minor  complications,  and  take  into 
account  the  main  features,  the  contours  of  the  land 
masses,  apart  from  the  modifications  produced  by 
denudation,  tally  with  the  slopes  which  would  be 
formed  as  the  result  of  the  various  uplifts  of  which 
we  have  independent  evidence.  The  structure  of 
the  lithosphere  beneath  the  oceans  is,  from  the  facts 
of  the  case,  hidden,  but  comparison  of  the  land  and 


FIG.  5. 
A.  Arch.     T.  Trough.     S.  Septum. 

ocean  features  shows  that  one  is  complementary  to 
the  other,  as  well  shown  in  Professor  Lapworth's 
address,  to  which  reference  has  just  been  made  : — 

"  The  surface  of  each  of  our  great  continental  masses  of 
land  resembles  that  of  a  long  and  broad  arch-like  form,  of 
which  we  see  the  simplest  type  in  the  New  World.  The 
surface  of  the  North  American  arch  is  sagged  downwards 
in  the  middle  into  a  central  depression  which  lies  between 
two  long  marginal  plateaux,  and  these  plateaux  are  finally 
crowned  by  the  wrinkled  crests  which  form  its  two  modern 
mountain  systems.  The  surface  of  each  of  our  ocean-floors 
exactly  resembles  that  of  a  continent  turned  upside  down. 
Taking  the  Atlantic  as  our  simplest  type,  we  may  say  that 
the  surface  of  an  ocean  basin  resembles  that  of  a  mighty 
trough  or  syncline,  buckled  up  more  or  less  centrally  into  a 
K 


50     SCIENTIFIC   STUDY   OF   SCENERY 

medial  ridge,  which  is  bounded  by  two  long  and  deep 
marginal  hollows,  in  the  cores  of  which  still  deeper  grooves 
sink  to  the  profoundest  depth.  This  complementary 
relationship  descends  even  to  the  minor  features  of  the 
two.  Where  the  great  continental  sag  sinks  below  the 
ocean  level  we  have  our  gulfs  and  our  Mediterraneans, 
seen  in  our  type  continent  as  the  Mexican  Gulf  and 
Hudson  Bay.  Where  the  central  oceanic  buckle  attains 
the  water-line  we  have  our  oceanic  islands,  seen  in  our 
type  ocean  as  St.  Helena  and  the  Azores.  Although  the 
apparent  crust-waves  are  neither  equal  in  size  nor  sym- 
metrical in  form,  this  complementary  relationship  between 
them  is  always  discernible.  The  broad  Pacific  depression 
seems  to  answer  to  the  broad  elevation  of  the  Old  World, 
the  narrow  trough  of  the  Atlantic  to  the  narrow  continent 
of  America." 

Similar  movements  on  a  smaller  scale,  as  will  be 
eventually  pointed  out,  account  for  our  mountain 
uplifts  and  valleys  of  depression,  and  even  the 
volcanoes  which  modify  portions  of  the  lithosphere 
owe  their  geographical  distribution  to  supplementary 
phenomena  connected  with  the  production  of  these 
great  earth- waves. 

If  a  continent  were  composed  exclusively  of 
stratified  rocks,  and  produced  by  one  uplift  of 
a  set  of  stratified  deposits  originally  laid  down 
horizontally  on  the  sea-floor,  and  if  the  uplift  were 
unaccompanied  by  denudation,  the  surface  of  the 
continent  would  be  completely  covered  by  the  upper- 
most stratum,  and  the  bedding  planes  separating 
the  strata  would  lie  in  curves  parallel  to  the 
surface  of  the  ground.  Study  of  our  continents 
indicates  that  they  are  of  a  much  more  complex 
character,  and  due  to  alternate  uplifts  above  and  de- 


CONTINENTS   AND   OCEAN    BASINS     51 

pressions  beneath  the  ocean  level.  Each  depression 
will  allow  of  the  accumulation  of  sediment ;  each 
uplift  raises  these  sediments  to  form  land,  and  as  that 
land  is  always  subjected  to  denuding  agents,  these 
sediments  will  be  partially  swept  from  the  land,  and 
the  edges  of  the  strata  will  abut  against  the  surface, 
just  as  if  we  curved  a  number  of  sheets  of  paper  into 
an  arch,  and  cut  off  the  top  of  the  arch :  the  edges  of 
the  sheets,  which  may  be  taken  to  represent  strata, 
would  abut  against  the  surface  produced  by  the 
cutting  process.  Subsequent  depression  would  admit 
of  the  deposition  of  more  horizontal  strata  on  the 
upturned  edges  of  the  earlier  ones.  Such  an 
arrangement  of  strata  is  known  to  geologists  as  an 
unconformity,  and  the  frequency  of  unconformities 
among  the  stratified  rocks  of  our  land  surfaces  shows 
that  many  portions  of  our  continents  have  been 
submerged  and  elevated  again  and  again,  and  that 
each  land  surface  is  as  a  rule  not  the  result  of  a 
simple  uplift,  but  that  they  have  grown  by  a  process 
of  accretion  of  fresh  masses  of  land  at  different  times. 
In  these  circumstances  it  will  be  well  to  leave  the 
actual  structure  of  our  main  land  surfaces  for  the 
present,  and  to  consider  the  events  which  would 
occur,  and  modify  the  land  masses,  if  we  commenced 
with  a  simple  uplift  of  horizontal  sediments. 

An  ideal  symmetrical  uplift  around  a  central  point 
would  give  rise  to  a  dome  -  shaped  mass  of  land 
highest  in  the  centre,  and  sloping  away  to  the  sea 
all  round,  with  a  coast-line  forming  a  perfect  circle. 
A  section  through  the  uplift  would  show  the  surface 
existing  as  a  simple  convex  curve,  and  the  planes  of 
stratification  beneath  it  running  parallel  to  the  curve 
as  shown  in  Fig.  6. 


52     SCIENTIFIC   STUDY   OF   SCENERY 

It  will  be  more  convenient,  however,  if  we  imagine 
the  uplift  as  occurring  around  a  horizontal  straight 
line  instead  of  above  a  point,  in  which  case  the  result 
would  be  a  long  ridge,  highest  above  this  axial  line, 
and  sloping  to  the  coasts,  which  in  our  imaginary 
continent  would  form  two  parallel  lines.  A  section 
of  this  uplift  at  right  angles  to  the  axial  line  would 
be  precisely  similar  to  the  section  across  the  dome, 
shown  in  Fig.  6. 

We  may  now  consider  the  relationship  of  the 
strata  to  the  continent.  The  axial  line  of  the  con- 
tinent is  also  that  of  an  anticlinal  arch  or  saddle  of 


FIG.  6. 
S  S'  =  Sea-level. 

the  strata,  and  the  strata  dip  away  on  either  side  of 
that  line  towards  the  coast,  while  the  strike  of  the 
strata  is  parallel  to  the  axial  line,  and  therefore  to 
the  longer  axis  of  the  ideal  land  mass.  It  will  be 
seen  that  the  main  watershed  is  immediately  above 
the  axial  line,  and  accordingly  the  primary  drainage 
system  of  the  continent  will  be  divided  along  a  line 
coinciding  with  that  from  which  the  strata  dip  on 
opposite  sides  in  different  directions.  The  rain 
falling  on  the  continent  will  determine  two  sets  of 
rivers,  running  from  the  watershed  to  either  coast. 
Thus,  in  the  case  of  a  simple  uplift,  there  is  a  direct 
connection  between  the  folding  of  the  strata  and  the 
initiation  of  the  river  system.  If  there  were  no 


CONTINENTS   AND   OCEAN    BASINS     53 

inequalities  on  the  surface,  the  rivers  would  run  as 
straight  lines  in  the  direction  of  the  dip  of  the 
strata  from  the  watershed  to  the  sea -coasts.1  It 
will  be  eventually  seen  that  these  rivers  cut  into  the 
strata  and  carve  valleys  for  themselves,  thus  ex- 
posing the  junction  between  different  strata  on  the 
earth's  surface,  and  also  producing  secondary  water- 
sheds between  adjoining  rivers.  Now,  the  strata  are 
of  different  degrees  of  hardness,  and  it  will  be  found 
that  the  tributary  streams  tend  to  cut  along  the 
softer  strata,  and  accordingly  run  at  right  angles  to 
the  primary  rivers,  and  parallel  to  the  strike  of  the 
strata.  The  primary  rivers  are  known  as  consequent 
streams,  being  consequent  upon  the  uplift,  while  the 
first-formed  tributaries,  which  we  shall  here  alone 
refer  to,  leaving  the  consideration  of  subsidiary 
streams  to  a  future  chapter,  are  termed  subsequent 
streams. 

The  formation  of  these  subsequent  streams  and 
their  valleys  will  give  rise  to  tertiary  watersheds 
separating  the  subsequent  streams,  and  accordingly 
in  the  case  of  a  symmetrical  and  simple  uplift,  such 
as  we  have  described,  a  river-system  of  the  following 
character  will  be  initiated  (Fig.  7). 

An  ideal  continent  then  owes  its  existence  and 
broader  physical  features  to  its  main  uplift ;  its 
mountain  masses  and  plateaux,  with  the  intervening 
broad  depressions,  are  due  to  the  formation  of  minor 
earth-waves ;  if  it  possesses  volcanoes,  they  will  pro- 
bably occur  with  definite  relationship  to  the  major 
uplift;  and  the  minor  features  are  due  to  sculpture 

1  All  the  primary  rivers  need  not  rise  at  the  watershed,  but  some 
may  rise  at  various  points  between  the  watershed  and  the  sea.  For 
the  sake  of  simplicity,  these  may  be  at  present  ignored. 


54     SCIENTIFIC   STUDY   OF  SCENERY 

by  denuding  agents,  and  to  occasional  accumulation 
mainly  in  the  hollows :  while  an  ideal  ocean  owes 
its  broad  features  to  its  main  depression ;  its  smaller 
elevations  and  depressions  are  due,  as  before,  to  minor 
earth-waves ;  volcanoes  may  modify  it,  and  its  coast- 


Coast, 


3  r 
1' 


GoasL 


_!--? 

i 

I;.. 

i_ 

*... 
i 


— i--- 


_U. 


,Llne 


-I-- 


2 

FIG. 


Line 


i,  i  =  Main  watershed.     2,  2  =  Secondary  watersheds. 
3,  3  —  Tertiary  watersheds. 

lines  will  be  affected  by  erosion  ;  but  the  principal 
minor  modifications,  unlike  those  of  the  land,  are 
produced,  not  by  denudation,  but  by  deposition, 
which  tends  to  fill  up  the  inequalities  by  the  forma- 
tion of  blankets  of  sediment,  producing  extensive 
plains  of  deposition  upon  the  ocean  floor,  ready  upon 
uplift  to  give  rise  to  portions  of  new  continents. 


CHAPTER  VI. 
MOUNTAINS 

IT  is  obvious  that  as  a  valley,  whether  of  move- 
ment or  of  erosion,  is  complementary  to  a 
mountain,  the  origin  and  structure  of  the  two  are 
closely  connected,  but  it  will  nevertheless  be  con- 
venient to  consider  the  two  apart,  though  the 
reader  will  remember  that  much  of  what  is  written 
concerning  mountains  must  be  taken  into  account 
when  considering  the  details  of  valley  structure  and 
valley  formation. 

Mountains  and  hills  have  been  classified,  accord- 
ing to  their  formation  : — (i )  by  accumulation;  (ii.)  by 
upheaval ;  (iii.)  by  circumdenudation.  The  hills  of 
accumulation  are  formed  by  piling  of  material  on 
the  earth's  surface,  and  the  chief  hills  formed  in 
this  manner  are  volcanoes,  while  minor  hills  of 
accumulation  are  known  as  sand-hills  or  sand- 
dunes.  Each  of  these  will  be  more  appropriately 
considered  in  later  chapters,  and  we  may  here 
confine  our  attention  to  the  hills  of  upheaval  and 
circumdenudation,  which  constitute  by  far  the  largest 
proportion  of  the  mountains  of  the  globe. 

It  is  convenient,  in  our  classification,  to  separate 

hills  of  upheaval,  produced  by  uplift  of  portions  of 

the  earth's   crust,  from    those  of  circumdenudation, 

due    to    the    erosion    of    portions    of    that    crust, 

55 


56    SCIENTIFIC   STUDY   OF   SCENERY 

thereby  leaving  intervening  portions  to  stand  out 
as  hills  above  the  general  level  of  the  eroded 
portions,  but  a  moment's  reflection  will  convince 
the  reader  that  an  ideal  hill  of  upheaval  or  of 
circumdenudation  cannot  exist.  The  agents  of 
erosion  affect  all  parts  of  the  surface  of  the  land, 
and  therefore,  however  nearly  a  hill  may  approach 
to  an  ideal  hill  of  upheaval,  it  must  owe  some  of 
its  surface  features  to  erosion,  whereas,  in  the  case 
of  strata  formed  beneath  the  ocean,  initial  uplift 
is  necessary  before  the  agents  of  erosion,  whose 
operation  is  essentially  restricted  to  the  land  masses, 
can  come  into  play.  Nevertheless,  as  some  hills 
owe  most  of  their  character  to  uplift,  and  others 
to  circumdenudation,  the  division  is  useful,  though 
it  must  be  distinctly  understood  that  a  complete 
gradation  can  be  traced  from  the  hill  which  is 
almost  entirely  due  to  uplift,  with  very  slight 
modification  due  to  erosion,  to  one  which  is 
blocked  out  by  erosion  from  an  elevated  tract  of 
plateau  region,  in  which  the  uplift  has  been  so 
uniform  that  the  outline  of  the  individual  hills  owes 
practically  nothing  to  uplift,  but  nearly  everything 
to  erosion. 

Our  study  of  hill  structure  will  be  simplified  if 
we  consider  the  effects  of  uplift  first,  and  those 
of  erosion  subsequently,  though  it  must  be  remem- 
bered that  in  nature  erosion  commences  with 
uplift,  and  operates  simultaneously.  As  soon  as 
the  future  hill-top  has  emerged  above  the  water, 
the  agents  of  erosion  begin  the  work  of  destruction, 
and  this  destruction  goes  on  while  further  emergence 
takes  place  ;  and  accordingly,  in  order  to  have  hills 
at  all,  the  uplift  must  occur  in  such  a  way  that 


MOUNTAINS  57 

erosion  cannot  keep  pace  with  it ;  otherwise  the 
potential  hill  would  be  reduced  to  a  level,  while  the 
rocks  of  which  it  was  composed  were  pushed  up. 

Before  discussing  the  variations  of  hill  structure 
produced  by  upheaval,  a  few  words  are  necessary 
concerning  the  rate  of  operation  of  upheaval  and 
other  agents  which  are  occupied  in  producing 
various  scenic  effects.  We  have  every  reason  for 
supposing  that  when  the  race  to  which  belonged 
the  flint  man  of  Abbeville  and  of  Kent's  Cavern 
occupied  Europe  the  occupants  gazed  on  hill  and 
vale  possessing  much  the  same  features  as  those 
which  they  now  present ;  and  if  a  palaeolithic  artist 
had  represented  Snowdon  or  Skiddaw  on  a  piece 
of  ivory,  its  outline  would  be  recognisable  as 
identical  with  that  which  it  at  present  exhibits  ; 
indeed,  long  before  the  appearance  of  man  in 
Britain,  the  physical  features  of  our  country  were 
essentially  those  of  the  present  time.  It  is  evident 
that  no  important  change  has  taken  place  in 
historic  times,  and  the  geologist  has  to  deal  with 
aeons  to  which  historic  times  are  but  as  a  day. 

No  definite  idea  of  the  duration  of  geological 
time  can  be  given  ;  its  vastness  becomes  impressed 
upon  one  as  the  result  of  observation  of  geological 
phenomena ;  the  geologist  finds  that  the  agents 
which  are  working  at  the  present  time  are  sufficient 
to  account  for  all  the  phenomena  of  the  stratified 
rocks  with  which  he  is  acquainted ;  but  finding 
how  slowly  these  agents  do  their  work,  and  how 
insignificant  are  the  changes  which  have  occurred 
during  periods  of  time  which  to  an  ordinary  man 
seem  enormous,  he  is  led  to  infer  that  immense 
periods  must  have  elapsed  in  order  to  explain  all 


58     SCIENTIFIC   STUDY   OF   SCENERY 

the  changes,  inorganic  and  organic,  with  which  he 
is  acquainted. 

The  casual  observer,  noting  the  strata  of  a 
mountain  slope  thrown  into  violent  folds,  zigzagging 
across  the  face  of  a  cliff  like  a  series  of  whip-lashes, 
might  easily  suppose  that  these  folds  are  due  to 
rapid  and  catastrophic  movements;  but  experiment 
will  show  that  under  ordinary  conditions  the  com- 
paratively rigid  rocks  cannot  be  bent  as  the  result 
of  sudden  application  of  pressure — they  will  snap 
across — whereas  if  pressure  be  applied  slowly  they 
may  be  bent  into  sharp  folds.  A  simple  experiment 
may  be  tried  with  an  ordinary  stick  of  sealing-wax. 
If  one  tries  to  bend  it  suddenly,  it  will  break  across  ; 
but  if  pressure  be  applied  very  slowly,  it  may  be 
bent  into  a  complete  circle  with  the  fingers  alone. 
Experiments  of  this  nature  do  not  necessarily 
indicate  that  folding  cannot  take  place  rapidly  when 
the  rocks  are  far  below  the  earth's  surface  and 
affected  by  the  pressure  of  thousands  of  feet  of 
superincumbent  rock,  but  they  show  that  under 
certain  conditions  rock  folding  can  be  produced  by 
slow  pressure,  and  not  by  rapid  movement,  and 
therefore  that  violent  contortion  of  the  strata  is  by 
no  means  proof  of  rapid  movement.  We  have  much 
further  evidence  of  the  slowness  of  movement  on  a 
large  scale,  but  it  is  beyond  our  scope  to  enter  fully 
into  this  question,  which  the  reader  will  find  discussed 
in  the  larger  works  devoted  to  the  study  of  geology. 

Passing  now  to  a  consideration  of  the  types  of 
uplift  which  give  rise  to  mountain  masses,  we  may 
divide  them  at  the  outset  into  two,  the  uplift  pro- 
duced as  the  result  of  folding  of  the  rocks  and  that 
due  to  fracture,  or,  in  other  words,  mountain  uplifts 


MOUNTAINS  59 

are  due  (i)  to  folding ;  (ii)  to  faulting.  It  will  be 
seen  in  the  sequel  that  the  one  is  often  accompanied 
by  the  other,  but  it  will  make  mountain-structure 
clearer  to  the  reader  if  we  omit  consideration  of  all 
complications  in  this  place,  and  take  ideal  forms  into 
consideration. 

Commencing  with  primary  forms  of  mountain 
masses  due  to  folding,  we  have  the  dome  and  the 
ridge,  the  former  being  the  result  of  the  bending 
of  the  strata  into  a  dome,  while  the  latter  is  caused 
by  their  curvature  into  a  saddle.1  The  symmetrical 
dome  is  comparatively  rare  on  a  large  scale,  and,  so 
far  as  we  know,  is  produced  by  vertical  upthrust  of 
strata,  especially  when  igneous  matter  in  a  state  of 
fusion  is  introduced  beneath  them.  If  this  matter  is 
brought  up  from  below  at  a  definite  point  and  forced 
between  strata,  it  will  tend  to  be  thickest  above  the 
point  at  which  it  enters  the  plane  of  stratification 
along  which  it  spreads,  and  to  thin  out  on  all  sides, 
so  that  it  would  have  the  general  shape  of  a  mush- 
room, the  stalk  being  represented  by  the  molten 
matter  which  flowed  up  the  pipe,  and  the  upper 
part  of  the  mushroom  by  the  mass  which  was  forced 
along  the  plane  of  stratification,  and  if  the  mass 
were  perfectly  symmetrical,  its  outline  would  be  a 
circle.  The  strata  would  be  arched  above  it,  the 
planes  of  stratification  lying  parallel  to  the  convex 
curve  of  the  surface  of  the  ground  and  also  to  the 
upper  surface  of  the  igneous  mass.  To  an  igneous 
mass  producing  an  elevation  of  this  nature  Dr.  G.  K. 

1  The  rocks  are  spoken  of  as  strata  for  convenience,  and  to 
emphasise  the  relationship  which  exists  between  surface  contours  and 
direction  of  planes  of  stratification,  but  it  must  be  noted  that  the 
component  rocks  of  mountain  masses  need  not  necessarily  be  stratified. 


6o     SCIENTIFIC   STUDY   OF  SCENERY 

Gilbert  has  given  the  name  laccolite,  and  as  laccolites 
present  us  with  the  most  symmetrical  cases  of  uplift 
known  to  us,  they  have  furnished  us  with  much  in- 
formation important  to  the  student  of  scenery,  and 
we  shall  frequently  have  occasion  to  refer  to  them 
hereafter.  The  typical  laccolites  are  found  constitut- 
ing the  Henry  mountains,  situated  in  Southern  Utah, 
and  are  described  by  Dr.  Gilbert.1 

The  ideal  ridge  will  differ  from  the  laccolitic  uplift, 
inasmuch  as  the  strata  are  bent  round  a  horizontal 
straight  line  instead  of  round  a  point,  but  a  cross- 
section  drawn  at  right  angles  to  the  axial  line  will 
show  a  convex  curve  similar  to  that  furnished  by 
a  cross-section  of  the  surface  of  a  laccolite.  It  will 
be  seen  that  the  ideal  ridge  does  not  exist  in  nature, 
for  it  would  go  completely  round  the  earth,  and  no 
mountain  chain  does  this.  The  ridge-like  elevations 
are,  strictly  speaking,  elongated  domes,  of  which  one 
axis  is  very  much  longer  than  the  other ;  but 
remembering  this,  it  will  be  simpler  to  treat  of  the 
structure  as  that  of  a  true  ridge,  to  which  it  often 
approximates  in  the  parallelism  of  its  two  sides  for 
very  long  distances.  The  symmetrical  ridge  is, 
however,  not  common  in  nature,  the  normal  ridge 
being  usually  steeper  on  one  side  than  on  the  other, 
as  in  the  ocean  wave,  where  the  septum  is  steeper 
than  the  other  slopes,  and  a  symmetrical  ridge  would 
really  be  a  combination  of  two  waves  with  a  trough 
on  each  side  of  the  uplift  Some  of  the  ranges  of 
the  Jura  mountains  approximate  to  the  type  of  a 
symmetrical  ridge. 

1  See  GILBERT,  G.  K.,  Geology  of  the  Henry  Mountains  (United 
States'  Geographical  and  Geological  Survey  of  the  Rocky  Mountain 
Region,  Washington,  1880),  a  work  to  which  frequent  reference  will  be 
made  in  these  pages. 


MOUNTAINS  61 

The  unsymmetrical  ridge  may  be  regarded  as  the 
normal  development  in  the  case  of  a  mountain  uplift. 
The  structure  in  this  case  is  identical  with  that  of 
the  ideal  uplift,  giving  rise  to  a  simple  continent  and 
ocean  basin,  as  seen  in  Fig.  5.  Uplifts  of  this 
character  are  specially  produced  as  the  result  of 
lateral  pressure,  and  they  tend  to  run  in  parallel 
waves,  giving  rise  to  parallel  mountain  chains  with 
intervening  valleys  of  depression.  The  degree  of 
departure  from  actual  symmetry  varies.  In  some 
cases  the  septum  is  steeper  than  the  other  slopes, 
but  is  not  vertical ;  in  other  cases  it  is  vertical,  and 


FIG.  8. 

sometimes  becomes  turned  over,  when  the  strata  of 
the  septum  are  reversed,  as  in  the  case  of  the  Mendip 
hills.  It  is  obvious  that  in  the  last  case  denudation 
must  produce  a  very  marked  influence  on  the  ultimate 
outline  of  the  mountain,  otherwise  a  huge  overhang- 
ing cliff  would  be  left  upon  the  mountain-side  where 
the  septum  occurs. 

In  the  case  of  uplifts  of  unconformable  strata,  the 
upper  strata  may  be  completely  denuded  in  the 
mountain  centres,  and  the  stratification  of  the  older 
rock  series  may  then  show  no  relationship  with  the 
axis  of  uplift,  as  shown  in  Fig.  8,  where  a  represents 
the  structure  before  denudation,  showing  the  relation- 
ship of  the  folding  of  the  upper  strata  with  the  axis 
of  uplift,  and  b  the  same  after  denudation,  the  former 


62     SCIENTIFIC   STUDY   OF   SCENERY 

extension  of  the  upper  strata  being  indicated  by  the 
curved  line.  This  complication  will  be  found  to  be 
important  when  we  enter  into  details  concerning 
mountain  and  valley  outline. 

Before  discussing  uplifts  due  to  fracture,  it  will  be 
necessary  to  say  a  few  words  concerning  the  minor 
folds  which  frequently  accompany  the  main  fold  pro- 
ducing an  uplift,  and  produce  very  marked  effects 
upon  the  features  presented  by  a  mountain  region 
such  as  the  Alps.  When  the  lateral  pressure  which 
produces  the  folds  is  comparatively  slight,  the 
minor  folds  are  often  fairly  symmetrical,  but  as  it 
increases  in  intensity,  the  earth-waves  are  compressed 
into  narrower  folds,  and  the  entire  rock  mass  loses 
greatly  in  horizontal  extension,  but  gains  proportion- 
ately in  height,  giving  origin  to  what  is  known  as 
a  mountain  range,  the  major  fold  forming  the  crest, 
and  the  harmonic  minor  folds  constituting  the  flanks 
of  the  range.1 

Now  towards  the  foot  of  this  range  the  minor  folds 
remain  fairly  symmetrical,  but  nearer  to  the  centre 
the  effect  of  the  lateral  thrust  and  counterthrust  is 
complicated  by  the  weight  of  the  mass  above,  which 
presses  the  upper  parts  of  the  minor  folds  towards 
the  base  of  the  mountain  range,  and  accordingly  the 
plane  surface  which  lies  between  the  axial  line  and 
the  summit  line  of  a  ridge  or  the  bottom  of  a  trough, 
which  is  vertical  in  the  case  of  a  symmetrical  uplift, 
is  forced  out  of  the  vertical  and  made  to  dip  inwards 

1  Quoted  from  a  paper  by  Professor  LAPWORTH  in  the  Geological 
Magazine,  dec.  ii.,  vol.  x,  entitled,  "The  Secret  of  the  Highlands," 
part  ix.  of  which  gives  a  summary  of  the  work  of  HEIM,  Mecha- 
nismus  der  Gebirgsbildung,  published  at  Zurich,  1878.  The  reader 
will  find  admirable  illustrations  of  Alpine  structure  in  the  aths  of  the 
latter  work. 


MOUNTAINS  63 

towards  the  centre  of  the  range,  and  the  strata  form- 
ing the  septum  of  each  wave  become  inverted.  This 
occurs  on  each  side  of  the  main  axis,  and  gives  rise 
to  the  well-known  fan  structure  which  characterises 
mountain  ranges  of  Alpine  type,  as  illustrated  in 
Fig.  9. 

This  fan  structure  may  be  repeated,  giving  rise  to 
a  mountain  system,  composed  of  more  or  less  parallel 
mountain  ranges,  each  of  which  is  composed  of  a 
central  crest  and  lateral  flanks.  Such  a  system  is 


FIG.  9. 

Showing  the  structure  of  a  mountain  range  of  Alpine  type,  without  denudation. 

found  in  the  Alps  complicated  by  countless  minor 
convolutions  and  fractures,  but  nevertheless  composed 
of  strata  so  arranged  as  to  allow  of  the  recognition 
of  the  fan  structure  on  a  large  scale.  For  instance, 
in  taking  a  traverse  from  north  to  south,  starting  at 
the  Lake  of  Lucerne  and  travelling  to  the  plain  of 
Lombardy,  we  traverse  three  definite  ranges  having 
a  general  fan  structure.  On  the  north  is  the  Aar 
range,  separated  from  the  central  Gotthard  range  by 
the  newer  rocks  of  the  Urserenthal,  while  the  Gott- 
hard range  is  separated  from  the  Tessin  range  on  the 
south  by  the  newer  rocks  in  the  valley  in  which 
Airolo  stands.  Similarly  to  the  west  of  this  the 
great  Bernese  Oberland  range  is  separated  from  that 


64     SCIENTIFIC   STUDY   OF   SCENERY 

of  the  Alps  of  the  Valais  by  the  upper  portion  of 
the  Rhone  valley,  containing  newer  rocks. 

There  is  one  type  of  unsymmetrical  fold  to  which 
allusion  has  not  yet  been  made  here,  known  as  the 
hogback,  or  monocline.  A  monocline  is  sometimes 
spoken  of  as  half  an  anticline  or  half  a  syncline, 
with  strata  on  either  side  of  it.  In  reality  a  mono- 
cline consists  of  a  complete  earth-wave,  the  septum 
of  which  is  inclined  at  a  high  angle,  while  the  other 
slopes  approach  to  horizontality.  The  monoclinal 
fold  gives  rise  to  steep,  curved  slopes  overlooking 
gently  sloping  surfaces,  as  typically  shown  in  the 
"hogbacks"  of  the  western  territories  of  North 
America.  When  two  hogbacks  occur  facing  in 
opposite  directions,  and  a  comparatively  level  tract 
between  them,  we  have  the  "  Uinta  type "  of  moun- 
tain folding,  typically  developed  in  the  Uinta 
mountains  of  North  America,  the  general  structure 
of  which  is  diagrammatically  shown  in  Fig.  10. 

In  summing  up  this  part  of  our  subject  we  may 
say  that  the  principal  types  of  mountain  structure 
produced  by  folding  are  as  follows : — 

i.  SIMPLE  TYPES. 
(a)  Symmetrical. 

(a)  Domes         .         .     e.g.  The  Henry  mountains. 

(b)  Symmetrical  saddles  „  Some  of  the  Jura  mountains. 

(c)  Uinta  type  .        „  The  Uinta  mountains. 

(b)  Unsymmetrical. 

(a)  Hogbacks         .         .     e.g.  The  "hogbacks"  of  the 

western  territories. 

(b)  Unsymmetrical  saddles,   e.g.  The  Mendip  hills. 

2.  COMPOUND  TYPE. 
Alpine  type     .        ;.         .     e.g.  The  Alpine  ranges. 


MOUNTAINS 


The  classification  is  not  altogether  satisfactory,  for, 
as  already  seen,  the  symmetrical  saddles  and  the  Uinta 
type  should  be  looked  upon  as  compounded  of  two 
earth-waves,  and  the  hogbacks  are  really  of  the 
nature  of  unsymmetrical  saddles,  of  which  one  slope 
is  so  small  as  to  appear  practically  horizontal,  but 
the  grouping  we  have  adopted  distinguishes  between 
different  types  each  of  which  exhibits  very  definite 
features,  and  the  features  of  those  types  which  are 
placed  in  the  same  subdivision  possess  important 
points  in  common. 


FIG.  10. 

We  may  now  proceed  to  consider  uplifts  which  are 
primarily  due  to  fracture,  and  must  observe  at  the 
outset  that  fracture  is  the  outcome  of  folding  carried 
to  excess,  so  that  the  strata  will  no  longer  yield  by 
bending.  If  a  rock  were  a  mathematically  rigid 
mass,  we  could  completely  separate  fracture  from 
folding,  but  in  a  mass  which  is  not  absolutely  rigid 
a  certain  amount  of  folding  precedes  fracture.  If 
one  examines  a  broken  iron  bar,  it  will  be  often 
seen  that  the  particles  of  the  bar  are  slightly  bent 
at  the  broken  part,  owing  to  the  production  of  an 
incipient  fold  before  fracture  occurs,  and  the  same 
is  often  noticeable  with  rocks.  Accordingly  every 
type  of  fold  has  its  accompanying  fault,  which  replaces 
the  septum  of  the  fold.  A  simple  earth-wave,  con- 
sisting of  saddle  and  trough,  where  the  strata  dip 


66     SCIENTIFIC   STUDY   OF   SCENERY 

away  from  the  axis  of  the  saddle  and  towards  the 
axis  of  the  trough,  has  its  septum  replaced  by  what 
is  known  as  a  normal  fault,  in  which  the  plane  of  the 
fault  dips  downwards  towards  the  side  of  the  trough, 
while  the  septum  of  an  overfolded  wave  or  sigmoidal 
flexure,  in  which  the  strata  of  the  septum  are  inverted, 
is  replaced  by  an  overfault  or  thrust-fault,  the  plane 
of  which  dips  downwards  towards  the  side  of  the 
saddle,  and  a  monoclinal  fold  or  hogback  is  replaced 
by  a  monoclinal  fault,  which  in  the  case  of  a  normal 
monocline  is  normal,  and  in  that  of  an  overfolded 
monocline  is  reversed.  This  is  illustrated  in  the 
following  figure. 


y 

s^  d, 


FIG.  ii. 


a   Symmetrical  Earth-wave. 

a'  Normal  Fault. 

b   Overfold. 

V  Faulted  Overfold. 


c  Normal  Hogback. 

c'  Monoclinal  Fault. 

d  Overfolded  Hogback. 

d'  Reversed  Monoclinal  Fault. 


The  main  difference  between  a  folded  uplift  and 
a  faulted  one  is  that,  whereas  the  fold  gives  a  convex 
surface  to  the  uplifted  region,  the  face  of  the  fracture 
tends  to  be  a  plane  surface,  having  the  inclination  of 
the  determining  fissure.  Accordingly,  if  denudation 
did  not  occur,  uplifts,  where  the  folding  is  replaced 
by  faulting,  would  be  marked  by  the  occurrence  of 


MOUNTAINS  67 

straight  cliffs.  It  is  clear  that  the  arrangement 
represented  in  Fig.  1 1  a  would  give  rise  to  a  hill- 
range  and  valley  of  depression  of  exactly  the  same 
nature  as  those  produced  by  the  arrangement 
Fig.  11  a,  except  for  the  difference  just  alluded  to. 
The  best  cases  of  ridges  and  valleys  determined  by 
fault  scarps  have  been  described  by  the  explorers  of 
the  western  territories  of  North  America.  These 
ridges  and  valleys  have  usually  been  profoundly 
modified  by  denudation,  but  the  features  due  to 
movement  are  still  ascertainable.  Admirable  ex- 
amples have  been  described  by  Professor  J.  W. 
Powell  in  his  Geology  of  the  Uinta  Mountains,  and 
the  nature  of  the  movements  and  the  resulting 
features  are  well  shown  in  Figs.  3  and  5  of  that  work. 
In  the  lower  part  of  the  latter  figure,  a  restoration 
of  part  of  the  region  is  given  showing  the  nature  of 
the  country  as  it  would  appear  if  displacement  had 
not  been  accompanied  by  denudation,  and  it  tallies 
very  well  with  the  actual  features  as  shown  in  the 
upper  portion  of  the  same  figure.  The  district  has 
been  broken  up  into  a  series  of  blocks  bounded  by 
rectilinear  margins — the  faults— and  differential  dis- 
placement of  these  blocks  has  occurred,  some  being 
elevated  as  compared  with  others,  and  also  portions 
of  one  block  being  tilted  up  more  than  others,  or 
one  portion  of  a  block  being  uplifted  and  another 
sagged  down.  The  country,  as  observed  by  Powell, 
much  resembles  the  surface  of  a  mass  of  ice  the 
blocks  of  which  are  "  crowded  in  an  eddy  of  a 
northern  river  at  the  time  of  its  spring  flood,"  and 
it  is  significant  that  a  district  of  the  character  we 
are  describing  is  often  marked  by  great  intrusions 
of  igneous  rock  forced  up  from  below,  so  that  the 


68     SCIENTIFIC   STUDY   OF   SCENERY 

structure  suggests  the  buoying  up  of  a  mass  of  the 
earth's  crust  above  a  reservoir  of  molten  rock  and 
settlement  of  the  cracked  parts  of  the  crust  to 
different  degrees  in  the  molten  mass  below. 

In  our  own  country  an  illustration  of  this  type  of 
displacement  is  furnished  by  the  Pennine  chain, 
and  it  is  especially  well  exhibited  in  the  northern 
part  of  the  chain,  which  overlooks  the  lower  part 
of  the  Eden  valley.  This  portion  of  the  Vale  of 
Eden  is  a  valley  of  depression,  separated  from  the 
uplift  of  the  Pennine  Chain  by  the  great  Pennine 
fault,  which  has  determined  the  existence  of  the  great 
scarped  cliff  which  faces  westwards,  a  cliff  specially 
noticeable  to  anyone  travelling  northwards  by  the 
main  Midland  line  between  Settle  and  Carlisle. 
The  present  features  are  due  to  denudation,  but  the 
uplift  of  the  Pennines  and  depression  of  the  Vale 
of  Eden  were  undoubtedly  determined  by  the  faulted 
earth-wave  which  exists  in  the  area. 

If  the  fault  be  small,  and  the  rocks  on  either  side 
easily  denuded,  the  fault  scarp  may  be  destroyed,  or 
never  called  into  existence.  For  instance,  the  Isle 
of  Wight  is  marked  by  a  monoclinal  fold  or  hog- 
back with  the  septum  partly  replaced  by  a  thrust- 
plane,  but  denudation  has  prevented  the  formation 
of  a  fault  scarp,  and  the  ground  on  the  uplifted  side 
of  the  fault,  though  higher  than  that  on  the  other 
side,  slopes  down  towards  it  with  a  comparatively 
small  gradient.  On  account  of  the  frequency  with 
which  denudation  has  levelled  the  ground  on  either 
side  of  a  fault  fissure,  English  geologists  have 
perhaps  been  prone  to  overestimate  the  power  of 
denudation  to  obliterate  all  inequalities  produced  by 
faulting.  In  areas  where  the  fracture  is  recent, 


MOUNTAINS  69 

especially  if  agents  of  denudation  are  not  very 
powerful,  as  in  desert  regions,  the  actual  cliffs  may 
be,  and  sometimes  certainly  are,  directly  due  to 
faulting,  as  shown  by  Gilbert  in  the  case  of  certain 
cliffs  of  the  Great  Basin  region  of  North  America, 
in  the  neighbourhood  of  Great  Salt  Lake. 

It  will  be  seen  that,  as  the  result  of  earth 
movement,  the  land  surfaces  would  possess  convex 
curves  among  the  hill  ranges,  and  concave  curves  in 
the  valleys  of  depression,  due  to  folding,  and  linear 
straight-faced  cliffs,  as  the  result  of  faulting.  The 
fact  that  these  surfaces  are  only  rarely  found  in- 
dicates that  the  existing  superficial  features,  though 
indirectly  due  to  earth  movement,  have  been  pro- 
foundly modified  by  other  causes,  and  it  remains  to 
be  seen  what  these  causes  are,  and  how  they  have 
produced  the  actual  features  presented  by  the  prin- 
cipal tracts  of  the  land  surfaces. 


CHAPTER   VII. 
MOUNTAINS    (Continued) 

HAVING  considered  the  general  structure  of 
mountain  ranges  and  mountain  systems,  we 
are  in  a  position  to  discuss  the  nature  of  the 
modifications  which  they  undergo,  and  the  character 
and  origin  of  individual  mountains.  As  the  result 
of  uplift,  mountain  ranges  are  caused,  but  if  the 
uplift  be  equal,  as  in  the  case  of  our  ideal  ridge, 
the  ridge  would  be  terminated  at  the  summit 
by  a  horizontal  line  —  the  watershedding  line — 
from  which  the  streams  would  flow  away  on  either 
side.  This  watershed  would  be  precisely  similar  to 
that  which  we  described  in  Chapter  V.,  as  forming  the 
main  watershed  of  a  continental  uplift,  and  the  drain- 
age would  be  initiated  and  secondary  watersheds 
developed  as  described  in  that  chapter. 

It  will  be  found  that  the  modifications  which  result 
in  the  formation  of  isolated  mountain  peaks  from 
mountain  ranges  are  due  to  the  agents  of  denudation, 
which  also  greatly  modify  the  general  character  of 
the  range  itself,  and  it  is  necessary,  therefore,  at 
this  point  to  pay  some  attention  to  the  effects  of 
denudation. 

We  noted  in  the  third  chapter  that  the  agents  of 
denudation  operated  in  the  dry  way  and  in  the  wet 
way  according  to  the  climatic  conditions  of  the 
70 


MOUNTAINS  71 

region  in  which  they  are  at  work.  Work  in  the  dry 
way  predominates  in  desert  regions  and  the  regions 
of  "  eternal  frost,"  though  even  there  the  effects  of 
water  are  not  entirely  eliminated,  but  over  the 
greater  part  of  the  earth's  surface  water  action  is 
dominant,  and  as  there  is  reason  to  suppose  that 
many  areas  now  affected  by  desert  conditions  and 
others  covered  by  a  mantle  of  snow  and  ice  were 
not  always  under  these  conditions,  we  must  admit 
that  the  action  of  water  is  of  paramount  importance 
in  effecting  denudation,  and  its  results  must  therefore 
be  considered  at  the  outset,  the  characteristic  features 
of  denudation  in  the  dry  way  being  discussed  sub- 
sequently. 

The  laws  of  water  denudation  have  been  very  fully 
illustrated  by  Dr.  Gilbert  as  a  result  of  study  of  the 
simple  conditions  which  exist  in  the  uplifts  of  the 
Henry  mountains,  and  much  of  the  following  de- 
scription is  abstracted  from  his  monograph  upon 
those  mountains.  It  has  already  been  stated  that 
the  mountains  are  in  the  form  of  domes,  marked  by 
intrusion  of  a  mushroom-shaped  mass  of  igneous  rock 
beneath  the  uplifted  strata,  but  it  will  be  convenient 
if  we  consider  the  case  of  drainage  impressed  upon 
an  ideal  ridge  rather  than  upon  a  symmetrical  dome. 

Watersheds. — The  ideal  ridge  consists  of  an  arch 
of  strata  bent  symmetrically  around  a  horizontal 
axial  line,  so  that,  if  it  be  supposed  that  the  ridge 
be  cut  in  two  along  a  vertical  plane  extending  from 
the  axial  line  to  the  parallel  horizontal  straight  line 
which  would  form  the  top  of  the  arch,  one  side  of 
the  ridge  would  be  the  exact  counterpart  of  the 
other,  and  its  surface  would  form  a  slope  approaching 
horizontality  towards  the  summit  (though  it  would  not 


72     SCIENTIFIC   STUDY   OF   SCENERY 

be  absolutely  horizontal  except  along  a  mathematical 
line—the  vvatershedding  line),  sloping  more  steeply 
at  some  distance  away  from  this  line,  and  approach- 
ing horizontality  towards  the  bottom  of  the  valley  of 
depression,  the  central  line  of  which  would  be  again 
horizontal,  so  that  the  steepest  part  of  the  mountain 
slope  would  be  the  centre  of  the  septum.  This  is 
shown  in  Fig.  12,  representing  a  section  across  the 
uplift. 

The  thick  line  a  a  indicates  the  ideal  surface  of  the 


ground,  b  the  strata  of  which  the  uplifted  tract  is 
composed,  c  the  point  at  which  the  axial  line  is  cut 
in  the  section,  d  the  watershed,  c  d  the  line  in 
which  the  bisecting  plane  is  cut  in  the  section,  e  e 
the  points  at  which  the  axial  lines  of  the  two  de- 
pressions are  cut  in  the  section,  f  f  the  sections  of 
the  lines  of  the  bottom  of  the  depressions,  and  g  g 
the  steepest  parts  of  the  slopes  at  the  centres  of  the 
septa. 

The  rain  which  falls  upon  the  actual  water- 
shedding  line  would  remain  stationary ;  there  is  no 
reason  why  it  should  flow  down  one  side  more  than 
the  other,  but  rain  falling  on  either  side  of  the  water- 


MOUNTAINS  73 

shedding  line  would  tend  to  flow  down  that  side. 
In  nature  the  water  as  a  rule  does  not  flow  directly 
it  reaches  the  ground,  for  all  rocks  can  absorb  water 
to  a  greater  or  less  extent,  and  consequently  the 
streams  which  course  down  the  mountain  -  side  do 
not  rise  absolutely  beside  the  watershed,  but  some 
little  distance  below  it  on  either  side.  We  rrfust  now 
state  a  very  important  principle,  to  which  we  shall 
have  to  refer  again  and  again,  namely,  that  when 
conditions  are  uniform,  and  agents  are  acting  with 
uniformity,  the  results  will  be  symmetrical,  and 
accordingly  all  departures  from  symmetry  must  be 
accounted  for  when  we  have  evidence  of  conditions 
which  are  generally  favourable  to  the  production  of 
symmetrical  features.  We  have  postulated  the 
existence  of  a  symmetrical  uplift  which  we  will 
suppose  to  affect  homogeneous  rocks,  and  if  the 
rainfall  is  uniformly  distributed  it  follows  that  the 
sources  of  the  streams  will  arise  at  points  equi- 
distant beneath  the  watershedding  line  on  either 
side,  and  that  these  points  must  be  equidistant  from 
one  another,  so  that  drainage  of  an  equal  area  of 
ground  which  has  absorbed  the  water  will  issue  from 
the  springs  at  which  the  streams  arise.  The  only 
symmetrical  arrangement  is  that  shown  in  Fig.  13, 
which  represents  a  plan  of  a  watershed,  x  y,  with 
springs  issuing  from  the  points  a  b  c ,  .  .  .  and  giving 
rise  to  streams  flowing  along  the  dotted  lines  in  the 
directions  indicated  by  the  arrows.  It  will  be  seen 
that  streams  rise  alternately  on  either  side,  and  that 
if  three  adjoining  points,  as  a  b  c  or  b  c  d,  be  joined 
by  lines,  the  resulting  figure  is  an  equilateral  triangle. 
It  will  be  ultimately  seen  that  the  streams  tend 
to  carve  out  valleys,  and  that  the  erosion  com- 


74     SCIENTIFIC   STUDY   OF   SCENERY 

mences  as  soon  as  the  water  issues  from  the 
spring,  and  accordingly  valleys  will  be  cut  along 
the  dotted  lines  in  Fig.  14,  and  the  ground  from 
a  b  downwards  along  the  dotted  lines  will  be 
rendered  appreciably  lower  than  the  ground  between 
the  springs  and  the  watershed.  The  action  of  the 

It  't  It  'I  't 

I  I  I  I  I 

1  I  I  I  I 

I  I  I  I  I 


\b 

1 

.f 

,A 

j* 

1 

1 

\ 

1 

i 

1 

1 

\ 

1 

1 

1 

1 

1 

1 

1 

ll 

ll 

ll 

ll 

ll 

FIG.  13. 

X,  Y  =  Watershed. 
a,  b,  e,  d,  e,f,  g,  ht  i,  k— Points  of  issue  of  water  from  springs. 

weather,  assisted  by  gravity,  will  prevent  the  for- 
mation of  a  vertical  cliff  above  a  b ;  material  will 
slip  down  from  the  ground  above,  and  be  carried 
away  by  the  stream  ;  and  half-funnel-shaped  valley 
heads  will  be  formed  around  the  springs,  each 
having  a  semi-circular  outline  in  plan,  the  springs 
marking  the  centres  of  the  semi  -  circles.  This 


MOUNTAINS 


75 


arrangement  is  shown  in  Fig.  14,  in  which  the 
zigzag  line  x  y  represents  part  of  the  primary 
watershed  (the  zigzag  character  of  which  we  are 
about  to  explain) ;  a  b  c  the  springs,  and  the 
dotted  lines  the  streams  flowing  from  them ;  /  2  j 
secondary  watersheds,  which  will  also  become  zig- 


FIG.  14. 

s  q  r  j-  y  =  Main  watershed. 
a  b  c  d  e  =  Points  of  origin  of  springs. 
i  2345  =  Secondary  watersheds. 

Dotted  semi-circles  =  Incipient  half-funnel-shaped  hollows. 
q  r  s  =  Culminating  peaks. 
/  u  v  w  =  Cuts  or  passes. 

zagged,  though  for  simplicity  they  are  represented 
as  straight ;  and  the  dotted  semi-circles,  the  summits 
of  the  half-funnel-shaped  slopes  above  and  around 
the  springs.  These  half-funnel-shaped  terminations 
of  valleys  are  frequent  on  a  large  scale  as  the 
cwms,  combes,  and  cirques,  which  form  so  marked 
a  feature  of  many  upland  regions.  As  the  valley 


76    SCIENTIFIC   STUDY   OF  SCENERY 

becomes  deepened,  the  funnels  will  be  cut  further 
and  further  back,  and  at  last  those  on  the  two  sides 
of  the  watershed  will  interfere  with  one  another, 
and  produce  a  change  in  the  direction  of  the  water- 
shed, which,  instead  of  remaining  straight,  will  now 
run  as  a  zigzag  line,  the  curves  becoming  converted 
into  straight  lines,  as  in  this  way  only  can  symmetry 
be  maintained;  the  watershed  will  now  run  along 
the  zigzag  q  r  s  y.  The  point  /,  in  the  centre  of 
the  line  x  q,  will  be  equidistant  from  the  points  a  b, 
and  accordingly  the  greatest  erosive  influence  will 
be  exerted  here,  and  less  and  less  erosion  will  take 
place  as  the  result  of  weathering  and  the  action 
of  gravitation  as  one  passes  along  the  line  to  points 
more  remote  from  a  and  b,  until  we  reach  x  and  q, 
where  the  least  erosive  influence  is  exerted ;  the 
points  x  and  q  are  situated  at  the  end  of  the  line, 
and  from  them  secondary  watersheds  extend  on 
either  side  of  the  main  one.  Accordingly  t  will  be 
the  lowest  point  of  the  portion  of  the  watershed 
represented  by  the  line  x  qy  and  x  q  the  highest 
points,  the  intervening  points  being  of  intermediate 
heights,  and  if  action  be  symmetrical,  the  line  will 
appear  in  section  as  a  curved  line.  Accordingly 
the  watershed  as  seen  in  section  will  present  the 
appearance  shown  in  Fig.  15,  the  letters  in  which 
correspond  with  those  of  the  plan  Fig.  14. 

This  change  in  the  character  of  the  watershed 
is  of  primary  importance  to  the  student  of  scenery, 
for  when  conditions  are  uniform,  and  symmetry 
therefore  maintained,  the  mountain-tops  will  appear 
at  the  heads  of  the  main  valleys,  while  the  cols  or 
passes  will  notch  the  watersheds  at  the  sides  of  the 
valleys,  and  from  two  adjoining  mountain  -  tops 


MOUNTAINS  77 

secondary  watersheds  will  extend  in  opposite 
directions.  In  nature  we  often  find  many  departures 
from  uniformity  of  conditions,  which  produce  marked 
modifications  of  the  ideal  watershed  described  above, 
but  there  are  a  very  large  number  of  cases  where  the 
departure  from  uniformity  is  too  slight  to  modify  the 
natural  arrangement  to  any  great  extent. 

As  an  illustration  of  the  production  of  the  arrange- 
ment of  mountain,  valley,  and  col  described  above, 
we  may  consider  the  district  in  the  neighbourhood 
of  Monte  Rosa,  which  shows  it  fairly  well,  though 
there  are  several  minor  complications.  Leaving  these 


FIG.  15. 

out  of  account,  we  have  the  Matterhorn  dominating 
the  head  of  the  Val  Tournanche,  and  sending  off 
the  secondary  watershed  on  which  the  Weisshorn 
is  situated.  (This  is  modified  by  the  line  of  weakness 
which  has  allowed  the  valley  in  which  the  Zmutt 
glacier  is  placed  to  cut  through  it.)  On  either 
side  of  the  Matterhorn,  at  the  upper  end  of  the 
Val  Tournanche,  we  have  a  lateral  col,  the  Col 
Tournanche  to  the  west,  the  Theodul  to  the  east. 
From  the  Matterhorn  the  watershed  trends  south- 
eastward to  another  culminating  point,  the  Breithorn, 
which  dominates  the  Visp  Thai,  and  sends  ridges 
to  the  south,  though  here  the  structure  is  com- 
plicated by  minor  valleys,  themselves  dominated 
by  minor  ridges,  and  accordingly  the  watershed 
does  not  turn  to  the  north  -  east,  as  it  would  if 
uniformity  had  prevailed.  The  next  culminating 


78     SCIENTIFIC   STUDY   OF  SCENERY 

point  is  Monte  Rosa  itself,  dominating  the  head 
of  the  Val  de  Gressonay,  and  sending  to  the 
northward  a  secondary  ridge,  which  culminates  in 
the  Mischabelhorner.  This  secondary  ridge  exhibits 
a  zigzag  watershed,  with  very  marked  approach 
to  symmetry,  the  culminating  points,  marking  the 
angles  of  the  zigzag,  occurring  in  the  following 
order  from  south  to  north :  Strahlhorn  ;  Rimpfisch- 
horn;  Allelinhorn;  Alphubel;  an  unnamed  point  just 
north  of  the  Mischabeljoch;  the  two  Mischabelhorner; 
Siid-Lenspitze;  Nadelhorn;  Ulrichshorn;  Balfrin.  It 
will  be  furthermore  noted  by  referring  to  a  map  that 
the  more  marked  ridges  are  given  off  alternately  from 
these  culminating  points  with  considerable  regularity. 

In  the  case  of  a  dome-shaped  uplift,  the  primary 
watershed  will  be  a  point  at  the  centre  of  the  dome, 
and  the  streams  and  secondary  watersheds  will 
radiate  from  this  point  like  the  spokes  of  a  wheel. 
The  drainage  of  the  English  Lake  District  is  deter- 
mined and  limited  by  watersheds  of  this  nature, 
though  more  symmetrical  domes  with  more  accurately 
radial  drainage  are  found  among  the  Henry  moun- 
tains. 

A  mountain  range  or  mountain  complex  consists 
of  mountains  sculptured  from  an  uplift  or  uplifts, 
of  which  the  height  is  usually  comparatively  small 
as  compared  with  the  length,  though  the  relation 
of  height  to  length  varies  considerably,  being  pro- 
portionately large  in  sharp  uplifts  of  Alpine  type, 
and  small  in  the  plateaux,  from  which  are  sculptured 
those  hills  which  most  truly  approach  the  ideal  hill 
of  circumdenudation.  Further,  the  height  of  neigh- 
bouring tracts  of  the  uplifts  will  not  vary  to  any 
great  extent,  and  accordingly  neighbouring  moun- 


MOUNTAINS  79 

tains  formed  by  the  sculpture  of  an  uplift  by  denuding 
agents  will  not  vary  in  height  to  any  great  extent, 
and  no  mountain,  except  one  of  accumulation,  can 
be  higher  than  the  surface  which  would  be  produced 
by  uplift  alone.  It  will  be  eventually  seen  that 
position  of  watersheds  may  change  owing  to  con- 
ditions of  asymmetry,  but  with  a  symmetrical  uplift, 
as  erosion  by  streams  on  the  watersheds  is  nil,  the 
watersheds  are  not  lowered  to  any  great  extent,  and 
the  mountains  which  are  carved  from  the  uplifted 
mass  tend  to  have  their  summits  remaining  for  long 
periods  at  a  height  not  much  lower  than  that  of  the 
original  watershed.  As  the  original  primary  watershed 
is  higher  than  any  parts  of  the  gradually  sloping 
secondary  watersheds,  the  mountains  situated  along 
the  line  of  primary  watershed  tend  to  be  higher  than 
those  situated  along  the  secondary  lines,  and  the 
latter,  under  uniform  conditions,  will  be  lower  and 
lower,  the  more  remote  their  position  is  from  the 
primary  watershed.  Thus  we  find  the  highest 
mountain  of  the  Alps,  Mont  Blanc,  on  the  primary 
watershed  of  the  complex,  and  the  highest  point 
of  the  Lake  District,  Scawfell  Pike,  situated  about 
the  centre  of  the  system  of  radial  drainage  lines. 
Taking  the  case  of  a  secondary  watershed,  that  which 
starts  between  the  Val  d'Herens  and  the  Val 
d'Anniviers,  in  the  Valais,  and  afterwards  separates 
the  two  branches  of  the  latter  valley,  though  modified 
by  complications  where  it  joins  the  main  watershed, 
has  the  following  crests,  varying  in  height  as  one 
passes  from  south  to  north,  away  from  the  main 
watershed: — Dent  Blanche,  4364  metres;  Grand 
Cornier,  3969  m. ;  Bouquetin,  3484  m. ;  Pigne  de 
1'Allee,  3404  m. ;  Garde  de  Bordon,  3316  m. 


8o     SCIENTIFIC   STUDY   OF   SCENERY 

Departure  from  uniformity  is  caused  by  a  number 
of  things,  among  which  may  be  mentioned,  as  of 
special  importance,  want  of  symmetry  in  the  uplifts, 
difference  of  structure  and  texture  of  the  rocks,  some 
of  which  are  more  easily  denuded  than  others,  and 
variation  in  the  character  and  amount  of  denudation 
in  different  places.  The  influence  of  these  in  pro- 
ducing variation  from  the  uniform  types  will  be 
considered  in  the  sequel.  Though  their  influence 
tends  to  complicate  the  ideal  structure  which  would 
be  produced  if  the  conditions  had  been  uniform,  this 
is  usually  only  masked,  and  not  destroyed,  and  when 
once  it  is  detected,  it  is  much  easier  to  account  for 
the  causes  of  departure  from  uniformity  than  would 
be  the  case  if  the  laws  of  mountain  formation  under 
uniform  conditions  had  not  previously  been  grasped. 

The  Three  Processes  of  Denudation. — Thus  far  we 
have  mainly  inquired  into  the  importance  of  uplift  in 
the  production  of  mountain  ranges  and  mountain 
systems,  and  have  only  referred  incidentally  to  the 
action  of  erosion  or  denudation.  We  have  now 
reached  a  stage  in  which  it  is  necessary  to  consider 
more  particularly  the  operation  and  influence  of  the 
erosive  agents. 

The  agents  of  erosion  are  many,  and  the  more 
important  may  be  grouped  as  follows  :  atmospheric 
or  meteoric  agents,  including  changes  of  temperature, 
wind,  and  rain  ;  streams  and  rivers  ;  glaciers  and  sea- 
waves.  As  previously  observed,  the  influence  of  rivers 
is  of  paramount  importance  to  the  student  of  scenery, 
not  only  on  account  of  the  capacity  of  individual 
rivers  as  agents  of  erosion,  but  -also  because  of  the 
great  frequency  and  general  distribution  of  rivers  over 
land  areas.  It  is  found  as  the  result  of  observation, 


MOUNTAINS  81 

and  might  readily  be  inferred,  that  rivers  erode  not  so 
much  by  the  direct  action  of  the  water  on  the  river- 
bed as  by  the  friction  of  the  sediment  transported  by 
the  river  against  the  rocks  which  compose  the  river- 
bed. Now  the  majority  of  rocks  are  in  a  solid  and 
compact  state,  with  their  particles  more  or  less  firmly 
welded  together,  and  before  they  are  in  a  condition 
for  transport  by  streams  they  must  be  broken  up. 
This  fracture  and  comminution  of  the  solid  rocks 
is  chiefly  carried  out  by  atmospheric  agents,  and  is 
therefore  spoken  of  as  weathering,  and  rock  weather- 
ing is  the  first  process  in  the  work  of  denudation. 
Detailed  accounts  of  the  effects  of  weathering  will  be 
introduced  more  appropriately  in  various  subsequent 
parts  of  this  volume.  It  is  sufficient  for  the  present  to 
understand  that,  as  the  result  of  weathering  action, 
we  are  furnished  with  a  supply  of  broken  and  com- 
minuted rock  material,  which  is  capable  of  being 
taken  up  and  washed  away  by  rivers.  The  latter 
process  is  spoken  of  as  transportation,  and,  owing  to 
gravitation,  the  transported  material  is  carried  from 
higher  to  lower  levels,  and,  if  unchecked,  ultimately 
to  the  sea,  where  it  settles  down  to  form  new  deposits. 
During  the  process  of  transportation  the  transported 
material  is  rubbed  and  knocked  against  the  bed  of 
the  river,  gnawing  it  away  and  thus  adding  to  the 
amount  of  material  to  be  transported,  and  at  the 
same  time  deepening  the  bed  of  the  river.  This 
action  is  termed  by  the  American  geologists  corrasion, 
a  term  which  is  coming  into  general  use.  The  three 
processes  of  ordinary  denudation  in  a  country  with  an 
abundant  supply  of  rainfall  and  drained  by  rivers  are, 
therefore,  weathering,  causing  the  comminution  of 
solid  rock,  transportation  of  comminuted  fragments 
G 


82     SCIENTIFIC   STUDY   OF   SCENERY 

of  particles,  and  corrasion  of  the  river-beds  by  these 
particles.  During  these  processes  the  larger  frag- 
ments have  their  asperities  knocked  off  and  are 
converted  into  rounded  pebbles,  and  the  finer  particles 
are  converted  into  grains  of  sand,  the  very  finest  into 
mud. 

Every  river  possesses  a  certain  amount  of  energy, 
which  enables  it  to  do  work,  and  the  work  which  it 
performs  is  of  a  twofold  nature,  namely,  transporta- 
tion and  corrasion.  Its  energy  is  not  unlimited,  and 
accordingly  every  river  can  only  do  a  certain  amount 
of  work,  which  may  be  entirely  transportation,  or 
transportation  and  corrasion,  according  to  circum- 
stances. The  amount  of  energy  of  any  river  depends 
upon  two  circumstances,  its  volume  and  its  velocity. 
Other  things  being  equal,  the  velocity  is  dependent 
upon  the  inclination  of  the  river-course ;  the  steeper 
the  slope  the  greater  the  velocity.  Now,  imagine 
a  river  running  down  a  uniform  slope  having  an 
angle  of,  say,  30°  along  all  parts  of  its  course, 
and  further  suppose  that  the  volume  of  this  river 
is  the  same  along  all  parts  of  that  slope.  Let  that 
river  be  supplied  with  the  exact  load  of  sediment 
which  it  is  capable  of  carrying,  neither  more  nor  less  ; 
all  the  energy  of  the  stream  will  be  utilised  in  carry- 
ing this  sediment,  and  no  energy  will  be  available 
for  the  process  of  corrasion.  Accordingly  the  river 
will  carry  its  material  along  the  slope,  and  no  other 
change  will  take  place.  Let  the  volume  and  velocity 
remain  as  before,  and  take  away  some  of  the  sedi- 
ment, and  some  of  the  energy  of  the  river  will  be 
rendered  available  for  corrasion,  and  the  bed  of  the 
river  will  be  corraded  by  the  remaining  sediment, 
and  though  the  slope  will  remain  uniform,  it  will 


MOUNTAINS  83 

be  lowered  by  corrasion  along  its  whole  extent.  If, 
instead  of  taking  away  sediment,  we  add  to  the 
original  amount  of  it,  the  river  will  be  supplied  with 
more  material  than  it  has  energy  to  transport,  and 
the  surplus  material  will  be  deposited  uniformly  upon 
the  slope  until  the  river  is  left  with  the  amount 
of  sediment  which  it  is  able  to  carry,  and  this  it  will 
transport  along  the  uniform  slope,  raised  above  its 
original  level  by  deposition  of  sediment. 

If  now,  instead  of  imagining  the  slope  to  be  a 
uniform  slope  of  30°,  we  suppose  that  the  average 
slope  is  at  that  angle,  some  parts  being  more  and 


FIG.  16. 


some  less,  as  shown  by  the  unbroken  zigzag  line 
in  Fig.  1 6,  and  further  imagine  that  the  river  is 
supplied  with  the  maximum  amount  of  sediment 
which  it  can  carry  without  corrading  or  depositing, 
if  its  slope  were  uniformly  one  of  30°,  then,  as  the 
parts  b  d,fh,  are  at  greater  slope  than  the  mean,  the 
velocity  of  the  stream  is  increased  along  here,  and 
corrasion  will  occur,  while  along  a  b,  df,  h  i,  the  slope 
is  less  than  the  average  slope,  and  the  velocity  of  the 
stream  will  be  diminished,  so  that  the  stream  cannot 
carry  all  its  load  along  these  portions,  but  will 
deposit  some  of  it.  These  processes  of  corrasion 
and  deposition  will  occur  along  the  alternating  steep 
and  gentle  parts  of  the  river-course  until  equilibrium 
is  established  and  the  stream  has  formed  a  uniform 


84     SCIENTIFIC   STUDY   OF   SCENERY 

slope  of  30°  by  the  erosion  of  the  portions  included 
in  the  triangles  a  be,  efg,  and  deposition  of  material 
to  fill  up  the  parts  shown  by  the  triangles  cde,  ghi. 
This  slope  will  form  a  straight  line,  a  c  e  g  z, 
corresponding  with  that  existing  in  our  original 
stream  of  uniform  slope,  and  on  the  establishment 
of  equilibrium  material  will  be  transported  as  before, 
neither  corrading  nor  being  deposited.  A  river  which 
has  established  equilibrium  in  this  way  is  said  to 
have  reached  its  base-line  of  erosion,  and  no  further 
work  of  erosion  or  deposit  can  occur  until  the  con- 
ditions are  changed,  causing  alteration  of  its  velocity, 
volume,  or  load  of  sediment. 

Our  ideal  uplift  presented  a  convex  curve  having 
different  slopes  along  different  portions  (see  Fig.  12), 
and  rivers  having  the  same  volume,  other  conditions 
being  equal,  would  tend  to  cut  valleys,  having 
uniform  slopes  along  the  valley  bottoms  until  the 
base-line  of  erosion  was  reached.  But  the  volume 
of  a  river  varies  along  different  parts  of  its  course, 
being  greatest  where  it  is  discharged  into  the  sea ; 
and  as  we  pass  up  from  the  sea  towards  the  source, 
and  leave  more  and  more  tributaries,  which  swell  its 
volume,  behind  us,  the  volume  of  the  main  stream 
becomes  less  and  less,  until  at  the  watershed  it  is 
nil.  Remembering  that,  other  things  being  equal,  the 
corrasion  varies  with  the  volume,  it  is  clear  that  cor- 
rasive  power  is  strongest  where  the  volume  is  greatest, 
and  there  the  river  will  make  its  slope  flatter,  while 
it  will  be  less  and  less  flat  where  the  volume  is 
smaller  and  the  corrasive  power  less.  Accordingly 
when  it  has  established  its  base-line  of  erosion  this 
line  will  be  a  curved  one,  ever  increasing  in  steepness 
from  the  sea  to  the  source.  If  we  imagined  two 


MOUNTAINS  85 

rivers  rising  opposite  to  one  another  in  the  watershed, 
a  section  along  their  courses  would  consist  of  two 
concave  curves,  as  shown  in  Fig.  17,  which  would 
replace  the  convex  curve  of  uplift  shown  by  the 
dotted  line. 

It  has  been  seen  that  at  the  extreme  summit  of  the 
river- courses  the  streams  rise  at  some  distance  below 
the  watershed,  and  the  degradation  of  the  ultimate 
slope  is  produced  by  weathering  and  slipping  of 
material  which  tends  to  lower  the  watershed,  though, 


FIG.  17. 

if  the  conditions  be  uniform,  it  will  be  situated  verti- 
cally below  its  original  position.  The  streams  in  the 
secondary  watersheds  will  act  in  the  same  way,  and, 
as  the  secondary  streams  have  their  velocity  increased 
by  increase  of  declivity  when  the  primary  stream 
lowers  its  level,  their  erosion  will  be  increased,  and 
the  secondary  watersheds  will  be  thus  modified,  and 
their  summits  tend  to  be  made  parallel  with  the 
curve  of  the  main  stream.  In  this  way  a  mountain 
uplift  will  be  carved  out  by  stream  erosion  into  a 
series  of  slopes  of  the  character  represented  in  Fig. 
17  ;  and  viewed  from  a  distance,  though  we  are  not 
looking  at  the  actual  stream  courses,  but  at  the 


86     SCIENTIFIC   STUDY   OF   SCENERY 

watersheds  occurring  between  adjoining  streams,  the 
outline  of  a  mountain  carved  out  by  water  erosion 
from  solid  rock  will  present  the  curves  seen  in  this 
figure.  As  erosion  progresses  the  curve  will  still 
remain,  though  it  will  be  rendered  flatter,  but  it  will 
always  retain  its  character,  being  flattest  at  the 
mouth  of  the  river  and  steepest  at  the  watershed. 
It  need  hardly  be  observed  that  the  curve  is  not 
confined  to  the  mountain  uplifts ;  it  must  be  pro- 
duced when  the  river  traverses  gently  sloping  ground, 
though  in  this  case  it  will  not  be  practically  dis- 
tinguishable from  a  straight  line. 

The  curve  of  river  erosion  produced  in  this  way 
may  be  modified  by  a  number  of  causes,  but  they 
usually  produce  minor  effects,  and  amidst  all  the 
variations  of  outline,  precipice,  scree-slope,  crag,  and 
pinnacle,  which  modify  mountain  slopes,  the  denu- 
dation curve  may  be  detected,  if  the  main  agent 
of  denudation  in  the  district  is  the  river,  and  the 
work  has  proceeded  for  a  period  of  time  sufficient  to 
enable  the  streams  to  establish  or  to  approach  to  the 
establishment  of  their  base  -  lines  of  erosion.  The 
importance  of  the  curve  of  river  denudation  as  in- 
fluencing mountain  scenery  cannot  be  overestimated. 
Mere  size,  though  impressive,  does  not  produce  the 
sense  of  beauty  which  is  felt  when  viewing  the  har- 
monious curves  of  hills  whose  outline  has  been  deter- 
mined by  stream  erosion.  The  adjoining  plate  is  a 
reproduction  of  a  photograph  of  the  Langebergen,  in 
Mossel  Bay  district,  Cape  Colony,  which  well  illus- 
trates the  outline  of  hills  whose  sculpture  has  been 
wrought  by  stream  erosion,  and  it  will  at  once  be 
seen  how  much  of  their  grace  they  owe  to  the 
beautiful  curvature  of  their  slopes. 


MOUNTAINS  87 

We  may  now  take  into  consideration  other  causes 
which  affect  mountain  outline  on  a  large  scale,  and 
first  may  take  note  of  hills  in  districts  which  are 
affected  by  stream  erosion,  which,  while  possessing 
the  curve  of  stream  erosion  in  the  basal  portion  at 
each  side,  present  a  convex  curve  at  the  summit,  as 
shown  in  Fig.  18  a.  This  is  a  very  common  outline, 
and  it  is  obvious  that  the  curve  of  erosion  is  modified 
or  replaced  by  a  curve  due  to  some  other  cause. 
I  have  for  some  years  taken  note  of  hills  possessing 
this  outline,  and  they  are  fairly  numerous  ;  the  Moels 
of  the  Welsh  hill  system,  as  Moel  Eilio,  between 
Carnarvon  and  Beddgelert,  show  it,  at  any  rate  on 


FIG.  18. 

one  side,  and  it  is  very  perfectly  shown  on  a  small 
scale  by  the  little  Dunmallet,  at  the  foot  of  Ullswater, 
and  by  the  larger  Mell  Fells  near  it.  In  all  cases 
where  I  have  observed  it,  the  portion  of  the  hill 
occupied  by  the  convex  curve  is  covered  by  vegeta- 
tion, often  by  a  thick  accumulation  of  peat,  while  the 
lower  part  exposes  bare  rock,  and  this  coincidence  is 
so  frequent  that  it  would  appear  that  the  change  of 
curve  is  produced  by  the  presence  of  vegetation. 
Now  where  this  vegetation  grows  corrasion  is  not 
taking  place,  or  bare  rock  would  be  exposed,  and  the 
action  of  weathering  is  dominant,  for  the  mass  of  soil 
is,  like  the  skin  of  the  body,  constantly  destroyed  on 
the  top,  replenished  from  beneath.  The  removal  is 
effected  by  wind  and  inconstant  rain  runnels,  the 


88     SCIENTIFIC   STUDY   OF   SCENERY 

renovation  by  weathering  of  the  rock  beneath.  It 
is  well  known  that  a  square  mass  tends  to  become 
rounded  by  weathering,  as  seen  in  the  granite  tors 
of  Devon,  and  as  can  be  experimentally  shown  by 
subjecting  a  cube  of  limestone  to  the  action  of  acid, 
or  more  simply  by  dissolving  a  cubical  block  of  sugar 
in  a  cup  of  tea,  for  at  every  edge  a  given  mass  pre- 
sents twice  as  much  surface  as  a  cubical  mass  of  the 
same  size  which  is  exposed  away  from  the  edge  of  a 
cube.  Thus  a  cube-shaped  mass  having  a  diameter  of 
one  inch,  forming  part  of  a  large  cube,  presents  two 
sides  having  a  diameter  of  one  inch  if  situated  at 
the  side  of  the  main  cube  and  only  one  if  away 
from  the  side,  while  it  exhibits  three  at  the  corners ; 
consequently  the  corners  wear  away  faster  than  the 
sides,  and  the  sides  faster  than  the  general  surface 
away  from  those  sides,  and  a  rounded  form  is  de- 
veloped. Now  if  we  suppose  a  block  of  country  of 
a  generally  rectangular  form  bounded  by  four  de- 
pressions, the  top  of  the  block  being  occupied  by 
vegetation,  in  the  absence  of  corrasive  action,  this 
block  would  be  modified  at  the  edges  and  corners  by 
weathering  action,  and  a  rounded  form  would  result. 
This  explanation  receives  confirmation  by  the  fre- 
quent occurrence  of  hills  having  the  outline  of  Fig. 
1 8  b,  where  one  side  has  the  true  water  erosion  curve 
to  the  summit,  while  the  other  exhibits  the  compound 
curve.  This  is  frequently  seen,  as,  for  instance,  on  the 
above-mentioned  Moel  Eilio  when  viewed  from  the 
north-west,  the  curve  of  water  erosion  being  on  the 
north-east  side,  facing  Llanberis,  while  the  compound 
curve  faces  the  south-west.  In  the  English  Lake 
District,  the  outline  is  frequently  seen,  as  in  Red 
Screes,  near  the  head  of  the  Kirkstone  Pass,  where 


MOUNTAINS  89 

the  eastern  face  possesses  the  stream-erosion  curve 
and  the  western  face  the  compound  one,  and  on  Steel 
Fell,  near  the  pass  of  Dunmail  Raise,  between  Win- 
dermere  and  Keswick,  where  the  respective  curves 
occupy  the  same  position.  The  rule  amongst  our 
British  hills,  where  this  outline  is  frequent,  is  that  the 
stream  curve  should  be  on  the  east  or  north-east  face 
of  the  hill,  and  the  compound  curve  on  its  west  or 
south-west  side.  It  is  well  seen  all  along  the  Hel- 
vellyn  and  High  Street  ridges  in  the  Lake  District, 
and  I  believe  that  it  is  due  to  the  fact  that  the 
south-west  slopes  in  our  country  are  under  meteor- 
ological conditions  allowing  of  extensive  growth  of 
vegetation  on  the  west  and  south-west  slopes,  while 
its  growth  is  checked  on  the  east  and  north-east 
sides. 

It  now  remains  for  us  to  consider  the  dominant 
outlines  of  mountains  in  regions  where  stream  erosion 
is  insignificant,  and  nature  works  in  the  dry  way, 
namely,  arctic  and  desert  areas.  Commencing  with 
consideration  of  arctic  regions,  we  have  the  arctic 
type  of  hill  outline  excellently  exhibited  in  the  case 
of  the  Greenland  hills.  It  can  hardly  be  supposed 
that  the  main  forms  of  the  mountains  have  been 
blocked  out  by  denudation  acting  in  the  dry  way, 
for,  in  the  absence  of  water  action,  we  know  of  no 
agent  which  is  capable  of  carving  out  valleys  and 
leaving  the  intermediate  portions  to  stand  out  as 
ridges  and  mountains.  Some  writers  have  asserted 
that  glaciers  are  capable  of  performing  this  work, 
but  we  shall  subsequently  see  reasons  for  supposing 
that  they  are  incapable  of  the  task.  We  must  there- 
fore suppose  that  a  country  like  Greenland  owes  its 
mountains  mainly  to  upheaval,  the  details  of  sculpture 


90     SCIENTIFIC   STUDY   OF   SCENERY 

only  being  executed  by  denuding  agents,  or  that  at 
some  far-distant  time  the  country  enjoyed  a  milder 
climate  than  its  present  one,  and  that  the  blocking 
out  of  the  individual  mountains  was  then  performed 
by  stream  erosion.  The  latter  supposition  is  more 
probable ;  but,  be  that  as  it  may,  inspection  of  the 
mountains  shows  that  their  present  outline  has  not 
been  determined  by  stream  erosion,  for  the  curve 
of  stream  erosion  is  absent  and  replaced  by  straight 
lines,  which  give  the  mountains  an  appearance 
which  is  aptly  described  by  the  term  applied  to 
this  structure,  namely,  "  house-roof  structure."  Illus- 
trations of  this  structure  have  been  given  by  A. 
Kornerup,1  and  it  is  very  well  shown  in  the  accom- 
panying plates,  of  a  hill  projecting  through  Norden- 
skjold  glacier,  and  of  Hornsund  Tind,  in  Spitsbergen, 
taken  from  photographs  kindly  furnished  by  Mr.  E.  J. 
Garwood. 

The  principal  agent  which  produces  this  structure 
is  frost,  acting  along  the  divisional  planes  of  the 
rocks.  The  water  percolates  along  these  divisional 
planes,  freezes,  and  in  so  doing  expands,  and  wedges 
off  angular  fragments  of  rock,  which  fall  down  the 
slopes  of  the  hills  and  accumulate  there,  forming 
screes.  We  have  already  seen  that  stratified  rocks 
are  specially  affected  by  three  sets  of  divisional 
planes,  namely,  planes  of  stratification,  and  two  sets 
of  joint -planes  at  right  angles  to  the  planes  of 
stratification  and  to  each  other.  Let  us  suppose 
that  the  planes  of  stratification  are  tilted  at  an  angle 
of  45°  in  one  direction  and  the  joints  at  the  same 
angle  in  the  opposite  direction  ;  the  frost  will  work 
along  these  planes,  and  produce  a  symmetrical 

1  Mcddeleher  om  Gronland,  part  ii.,  plate  vii. 


MOUNTAINS  91 

mountain  with  house -roof  structure,  as  shown  in 
Fig.  19  a,  whereas  if  the  planes  of  stratification  are 
less  inclined  and  the  joint-planes  at  a  greater  in- 
clination the  resulting  mountain  will  be  unsym- 
metrical,  as  in  Fig.  19  b. 

In  some  parts  of  Greenland  this  house-roof  structure 
has  been  brought  to  a  very  perfect  state  as  the  result 
of  frost  action,1  and  the  higher  peaks  of  Spitsbergen 
show  it  very  well,  though  the  stream  line  of  erosion 


is  often  found  in  the  lower  parts  of  the  islands,  where 
stream  action  is  very  pronounced.  (See  frontispiece). 
The  upper  peaks  and  aiguilles  of  the  Alps  are  also 
frequently  marked  by  the  possession  of  house- roof 
structure,  but  there  is  every  reason  for  supposing  that 
at  no  distant  date  the  Alps  were  subject  to  the  action 
of  ordinary  stream  erosion  in  parts  which  are  now 
permanently  above  the  snow  line  and  occupied  by 

1  In  parts  of  Greenland,  valleys  with  parabolic  section  are  found, 
and  appear  to  be  due  to  denudation  of  rocks  effected  by  a  curved 
system  of  joints.  See  figure  by  KORNERUP,  Meddelelser  om  Gronland^ 
part  L,  fig.  1 6. 


92     SCIENTIFIC   STUDY   OF   SCENERY 

snow  and  ice,  and  the  curves  of  water  erosion  in 
many  cases  do  not  seem  to  be  completely  obliterated, 
though  partly  masked,  by  the  subsequent  action  of 
frost.  The  outline  of  the  Dents  de  Veisivi  shows 
the  frost  outline  very  well  as  seen  from  Evolena,  as 
does  also  the  beautiful  Dent  Blanche,  on  the  opposite 
side  of  the  Ferpecle  glacier,  and  a  very  perfect  example 
of  a  frost- formed  aiguille,  the  Aiguille  de  la  Za,  is 
seen  on  the  ridge  of  which  the  Veisivis  form  the 
termination. 

Denudation  in  desert  regions  is  also  carried  on 
essentially  in  the  dry  way,  and  though  the  agents 
are  different,  the  resultant  mountain  forms  are  similar 
to  those  of  arctic  regions.  The  differences  of 
temperature  between  day  and  night  are  very  pro- 
nounced, as  radiation  at  night  causes  the  temperature 
to  fall  to  a  low  point,  and  the  rocks  are  subject  to 
alternate  expansion  during  the  heat  of  the  day  and 
contraction  during  the  cold  nights,  which  causes 
large  fragments  to  split  off  the  cliffs  and  fall  to  a 
lower  level. 

"Dr.  Livingstone  found  in  Africa  (12°  south  latitude,  34° 
east  longitude)  that  surfaces  of  rock  which  during  the  day 
were  heated  up  to  137°  Fahr.  cooled  so  rapidly  by  radiation 
at  night  that,  unable  to  bear  the  strain  of  contraction,  they 
split  and  threw  off  sharp  angular  fragments  from  a  few 
ounces  to  100  or  200  pounds  in  weight.  In  the  plateau 
region  of  North  America,  though  the  climate  is  too  dry 
to  afford  much  scope  for  the  operation  of  frost,  this  daily 
vicissitude  of  temperature  produces  results  that  quite  rival 
those  usually  associated  with  the  work  of  frost.  Cliffs  are 
slowly  disintegrated,  the  surface  of  arid  plains  is  loosened, 
and  the  fine  debris  is  blown  away  by  the  wind."  * 

1  GEIKIE,  Sir  A.,  Text-book  of  Geology,  3rd  edition,  p.  329. 


MOUNTAINS  93 

The  wind  in  these  regions  plays  the  part  of  trans- 
porting agent  in  lieu  of  the  rivers  of  areas  enjoying 
a  humid  climate  or  the  glaciers  of  arctic  regions, 
and  clears  away  the  debris,  which  would  otherwise 
accumulate  to  such  an  extent  as  to  mask  the  solid 
rock  over  which  it  lay. 

We  have  now  considered  the  main  causes  of  the 
general  features  of  mountains  of  upheaval  and 
circumdenudation.  Ridges,  domes,  and  plateaux  are 
uplifted  owing  to  earth  movements,  and  these  are 
alike  sculptured  by  surface  agencies,  so  that  a  series 
of  minor  ridges  is  developed  in  the  direction  of  the 
greatest  slopes,  while  both  the  primary  ridge  of  a 
simple  saddle-shaped  uplift  and  the  minor  ridges 
determined  by  the  formation  of  the  consequent 
valleys  are  further  carved  into  individual  peaks, 
separated  from  each  other  by  cols  or  passes. 


CHAPTER   VIII. 

MOUNTAINS   (continued} 

E  TAILS  of  Mountain  Structure.  —  We  have 
seen  that  two  primary  types  of  mountain  out- 
line exist,  according  as  the  mountain  mass  has  been 
hewn  out  of  the  solid  block  by  the  sculpturing  action 
of  running  water,  without  modification  by  any  other 
agent,  when  the  double  denudation  curve  is  pro- 
duced, or  whether  it  has  been  finished  in  the  dry 
way  by  the  action  of  frost,  or  by  alternate  expansion 
and  contraction  owing  to  rapid  and  marked  changes 
of  temperature.  The  characters  of  mountains  formed 
according  to  the  two  types  are  recognisable  at  a 
distance,  but  when  we  are  on  the  mountain  the 
general  outline  is  often  concealed,  and  we  notice 
minor  effects,  which,  though  on  a  small  scale  as  com- 
pared with  the  bulk  of  the  mountain,  are  sufficiently 
important  to  produce  a  marked  influence  on  the 
scenery.  A  cliff  500  feet  high  on  a  mountain  15,000 
feet  high  may  appear  as  a  mere  notch  at  a  distance, 
hardly  affecting  the  general  character  of  the  moun- 
tain outline,  but  when  we  are  stationed  near  the 
base  of  that  cliff  it  is  an  object  sufficiently  imposing 
to  contemplate  with  feelings  of  awe. 

The  minor  features  of  mountain  ranges  and  moun- 
tain-masses are  due  to  two  principal  causes,  namely, 
the  character  of  the  sculpturing  agent  and  the  nature 
94 


MOUNTAINS  95 

and  structure  of  the  component  rocks.  The  influence 
of  these  we  may  now  proceed  to  consider. 

Influence  of  the  Sculpturing  Agents. — Little  need 
be  added  here  to  what  has  already  been  said  con- 
cerning these,  for  the  effects  which  are  produced  on 
a  large  scale  are,  to  some  extent,  repeated  on  a 
smaller  one.  Running  water  when  passing  over  a 
surface  consisting  of  alternate  hard  and  soft  rocks, 
before  it  has  established  its  general  base-line  of  erosion, 
frequently  establishes  a  temporary  series  of  such  base- 
lines in  the  soft  rocks,  leaving  the  harder  nearly  in 
their  original  state  for  some  time ;  accordingly  we 
frequently  find  a  mountain-side  defined  by  alternate 
precipices  and  curves  of  erosion.  The  work  of  frost, 
though  most  marked  in  Arctic  and  Alpine  regions,  is 
sufficiently  pronounced  in  the  upland  districts  of  our 
own  country  on  a  small  scale,  and  we  find  miniature 
house-roof  structure  and  aiguilles  among  the  hills  of 
our  island.  The  climbers  who  visit  Wasdale  Head, 
in  the  Lake  District,  to  whom  the  Great  Gable  is  so 
familiar,  need  not  be  reminded  of  the  appearance  of 
the  roof-like  "Arrowhead  Rock"  or  the  aiguille-like 
"  Napes  Needle,"  which  furnish  us  with  excellent 
examples  of  mountain  detail  produced  by  the  action 
of  frost. 

The  effect  of  wind  is  specially  marked  in  desert 
regions,  and  we  shall  pay  attention  to  it  at  greater 
length  when  considering  deserts,  but  its  action  is 
sometimes  noticeable  on  a  small  scale  in  our  own 
country.  The  wind  sweeps  particles  of  sand  near 
the  ground,  and  carries  them  against  the  rock  like 
a  sand  blast,  fretting  away  the  rocks,  especially  along 
the  divisional  planes,  such  as  planes  of  stratification 
and  joints,  and  accordingly  we  get  fantastic  pillars 


96     SCIENTIFIC   STUDY   OF   SCENERY 

formed  with  undercut  bases  standing  from  the  cliffs, 
as  seen  in  the  case  of  the  well-known  Brimham  Rocks, 
carved  out  of  the  millstone  grit  of  West  Yorkshire. 

The  fragments  split  from  the  cliffs,  whether  by 
frost  or  by  alternate  contraction  and  expansion  of 
the  rock  surfaces,  accumulate  at  the  bases  of  pre- 
cipices as  screes,  which  often  form  apparently 
straight  lines,  corresponding  with  the  maximum 
angle  at  which  the  loose  fragments  can  rest.  These 
screes  frequently  form  prominent  features  of  a  scene  ; 
witness  the  well-known  screes  of  Wastwater,  which 
rise  about  1500  feet  above  the  lake  of  that  name. 
(See  plate  in  a  later  chapter.)  Screes  which  accumu- 
late at  the  bottom  of  a  valley  often  possess  an  outline 
similar  to  that  of  the  curve  of  water  erosion,  and  as 
the  stream-courses  often  branch  from  the  top  of  the 
screes,  and  run  in  many  ramifications  down  them,  it 
might  be  supposed  that  the  volume  of  the  individual 
runlets  decreased  from  top  to  base,  and  that  a  convex 
curve  should  be  produced ;  but  although  the  stream - 
courses  ramify,  the  discharge  of  water  usually  takes 
place  down  one  watercourse  at  a  time,  so  that  the 
action  of  water  may  be  neglected,  and  the  curved 
form  appears  to  be  one  normally  produced  by  a  self- 
supporting  pile  of  loose  blocks,  which,  under  the 
influence  of  its  own  weight,  tends  to  spread  outwards 
at  the  base ;  the  larger  fragments  also  tend  to  roll 
further  down  the  slope  than  smaller  ones,  as  they 
present  less  surface  compared  with  their  mass,  and 
consequently  are  not  so  easily  arrested  owing  to 
friction.  These  changes  give  rise  to  a  logarithmic 
curve.1  We  find,  therefore,  that  the  apparently 

1  See  MILNE,  Professor  J.,  "On  the  Formation  of  Volcanoes,"  Geol. 
Mag.t  dec.  ii.,  vol.  vi.,  p.  506. 


MOUNTAINS  97 

straight  lines  are  not  actually  straight  when  closely 
examined,  but  form  portions  of  a  curve  which  ap- 
proaches most  nearly  to  the  straight  line  near  the 
summit  of  the  screes,  and  rapidly  flattens  out  near 
the  base,  and  this  is  true  of  screes,  whether  accumu- 
lated along  a  considerable  line  of  cliff  or  forming  a 
detrital,  semi-conical  mass,  whose  apex  is  situated  at 
the  bottom  of  a  gully  or  scree- shoot,  from  which  the 
material  is  discharged,  sometimes  by  running  water, 
at  other  times  owing  to  the  action  of  frost  and  other 
weathering  agents. 

Other  variations  than  those  we  have  considered, 
which  are  due  to  differences  in  the  nature  or  mode 
of  operation  of  the  sculpturing  agent,  are  largely 
affected  by  the  composition  and  structure  of  rocks, 
which  we  may  now  proceed  to  consider. 

Influence  of  Rock  Composition  and  Structure. — 
Apart  from  all  minor  considerations,  and  whatever 
be  the  agent  of  denudation  which  is  at  work  upon 
rocks,  it  may  be  laid  down  as  a  general  law  that 
rocks  are  denuded  to  a  greater  or  less  extent 
according  to  their  relative  durability ;  the  harder 
rocks  tend  to  resist  denudation,  and  the  softer  ones 
to  be  worn  away.  As  the  ultimate  result  of  subaerial 
denudation  (i.e.,  of  that  denudation  which  is  carried 
out  over  the  general  surface  of  the  land  by  frost, 
rain,  rivers,  etc.,  as  opposed  to  marine  denudation, 
which  is  performed  along  coast-lines  by  the  agency 
of  the  sea)  is  to  reduce  a  country  to  a  general  base 
level  of  erosion  which  is  so  nearly  a  plain  that  it 
would  be  undistinguishable  from  one  by  the  eye — 
such  a  plain  has  been  termed  a  peneplain  by  Professor 
W.  M.  Davis — and  as  a  peneplain  would  be  produced 
in  softer  rocks  much  more  quickly  than  in  those  of 


98     SCIENTIFIC   STUDY   OF   SCENERY 

more  durable  texture,  it  is  evident  that  hard  rocks 
are  likely  to  stand  out  as  elevations  in  a  country 
which  has  been  subjected  to  denudation  for  long 
periods  after  the  soft  rocks  have  been  reduced  to  a 
peneplain.  Accordingly  most  hilly  regions  are 
composed  essentially  of  hard  rocks,  though  there 
are  wide  variations  in  the  relative  durability  of  the 
rocks  which  compose  these  regions,  as  well  as  those 
of  the  flatter  tracts.  Among  the  harder  rocks  the 
most  noticeable  are  crystalline  rocks,  as  granite, 
basalt,  and  the  crystalline  schists,  also  many  sand- 
stones and  limestones,  while  consolidated  muds  and 
clays  constitute  the  most  important  softer  rocks. 
But,  apart  from  the  actual  durability  of  the  rock 
substance,  denudation  is  profoundly  affected  by  the 
character  of  the  divisional  planes  which  traverse  the 
rocks,  and  these  are  of  the  utmost  importance,  as 
determining  the  details  of  scenery  in  both  moun- 
tainous and  more  level  districts.  It  will  be 
impossible  to  separate  completely  the  effects  of 
rock  composition  and  rock  texture  from  those  which 
are  determined  by  the  divisional  planes  which  run 
through  rock  masses,  but  we  may  do  so  to  some 
extent,  and  begin  with  a  consideration  of  the  in- 
fluence of  rock  composition  and  rock  texture  upon 
scenery  of  mountain  districts,  premising  that  much 
that  is  said  concerning  this  and  also  about  the 
divisional  planes  applies  equally  to  the  scenery  of 
lowland  districts. 

Beginning  with  the  igneous  rocks,  we  may  note, 
in  the  first  place,  that  their  influence  upon  scenery 
is  specially  determined  by  their  composition,  and  by 
the  conditions  under  which  they  have  consolidated. 
The  composition  is  not  only  important  on  account 


MOUNTAINS  99 

of  the  different  effects  produced  upon  rocks  of 
different  composition  by  the  agents  of  denudation, 
but  also  because  the  distribution  of  the  rock  mass 
is  affected  by  its  composition.  Igneous  rocks  are 
divided  into  two  main  classes,  according  to  their 
composition,  namely,  the  acid  class  and  the  basic 
class ;  the  rocks  of  the  former  contain  a  much  larger 
percentage  of  silica  than  those  of  the  latter,  and 
rocks  of  the  acid  class  are  generally  fusible  at  a 
lower  temperature  than  those  of  the  basic  class. 
Accordingly  the  acid  rocks,  whether  erupted  on  the 
earth's  surface  or  forced  between  masses  of  rock 
below  the  surface,  do  not  as  a  rule  spread  far  from 
the  place  at  which  they  are  intruded  or  extruded, 
for  they  cool  quickly ;  whereas  the  more  slowly 
cooling  basic  rocks  frequently  spread  over  a  wide 
area  before  finally  becoming  solid.  Acid  rocks 
accordingly  occur  very  frequently  in  massive  bosses, 
while  the  basic  rocks  are  apt  to  give  rise  to  extensive 
sheets  of  rock,  of  no  great  thickness  as  compared 
with  their  horizontal  extent,  and  having  their  two 
limiting  surfaces  approximately  parallel.  There  are 
many  exceptions  to  this  rule — for  instance,  in  Skye 
and  Mull  great  masses  of  basic  rock  are  found  as 
irregular  bosses — but  taking  the  two  widespread 
types  of  the  two  classes,  namely,  the  acid  granite 
and  the  basic  basalt  (using  these  terms  in  a  some- 
what general  sense),  we  find  that  they  conform  fairly 
closely  to  the  above-mentioned  conditions.  We  find 
accordingly  that  the  granitic  type  of  rock  is  often 
carved  into  massive  hills  and  mountains,  while  the 
basaltic  type  frequently  forms  terraced  hills  and 
plateaux. 

The   texture    of   igneous    rocks    differs   with    the 


ioo    SCIENTIFIC   STUDY   OF   SCENERY 

conditions  under  which  they  have  consolidated,  rocks 
being  coarsely  crystalline,  finely  crystalline,  or 
glassy,  according  as  they  have  been  cooled  very 
slowly,  fairly  slowly,  or  rapidly,  and  the  difference 
of  texture  naturally  produces  some  effect  upon  the 
action  of  the  denuding  agents,  though  no  general 
rule  can  be  laid  down  under  this  head,  for  difference 
of  texture  is  comparatively  unimportant  as  in- 
fluencing the  structure  of  mountains  upon  a  large 
scale. 

Of  greater  importance  is  the  shape  of  the  igneous 
mass,  which  is  due  to  the  mode  of  intrusion  or 
extrusion.  Intrusive  rocks  may  occur  as  irregular 
bosses  or  laccolitic  masses,  which  give  rise  to  irregular 
or  dome-shaped  eminences  when  left  standing  as 
elevations  owing  to  denudation  of  the  softer  rocks 
around,  or  they  may  be  forced  into  vertical  or  nearly 
vertical  cracks  as  joints  or  fault-planes,  forming 
igneous  dykes,  or  along  horizontal  or  nearly  horizontal 
planes  of  bedding,  forming  intrusive  sheets  or  sills,  or 
they  may  be  poured  out  on  the  surface  as  lava  sheets, 
or,  finally,  they  may  fill  the  approximately  cylindrical 
shaft  of  a  volcano.  The  horizontal  or  nearly  hori- 
zontal sheets,  often  alternating  with  softer  rocks, 
may  be  treated  as  hard  strata,  and  produce  the 
same  effects  on  a  large  scale.  The  cylindrical  plugs, 
often  surrounded  by  a  hardened  mass  of  baked  rock, 
frequently  resist  denudation,  and  stand  out  as  marked 
elevations,  after  the  surrounding  rocks  have  been 
worn  away. 

The  dykes  merit  a  somewhat  fuller  consideration. 
They  are  forced  between  rocks  as  wall -like  masses, 
and  their  effect  upon  scenery  depends  to  a  great 
extent  upon  their  chemical  composition.  The 


MOUNTAINS  101 

processes  of  weathering  are  conducted  in  two  ways, 
either  mechanically  or  chemically.  Hitherto  we 
have  not  referred  to  the  effects  of  chemical  change 
on  rock  weathering,  but  as  it  produces  marked 
influence  on  the  character  of  the  scenery,  it  is 
necessary  to  refer  to  it,  and  this  is  the  most  con- 
venient place  in  which  to  consider  it,  as  different 
kinds  of  rock  are  affected  by  the  weather  in  different 
ways. 

The  rain  which  falls  upon  the  earth  is  charged 
with  various  solvent  substances,  the  most  important 
of  which  is  carbonic  anhydride  (carbonic  acid  gas), 
and  the  water  falling  upon  soil  containing  vegetable 
matter  extracts  other  solvent  acids,  so  that  this 
acidulated  water  is  capable  of  dissolving  certain 
rock  constituents.  In  the  case  of  many  of  the 
sedimentary  rocks,  the  materials  of  which  they  are 
composed  have  frequently  been  subjected  to  the 
action  of  carbonated  waters  at  different  times,  and 
much  of  the  more  soluble  material  has  been  leached 
out  of  them  ;  but  the  igneous  rocks,  brought  from 
the  earth's  interior,  contain  much  soluble  matter,  and 
acidulated  surface  waters  are  capable  of  producing 
marked  changes  in  them  in  certain  circumstances. 
Some  igneous  rocks  yield  to  the  chemical  action 
of  the  weather  more  readily  than  others  ;  and 
accordingly,  in  the  case  of  dykes,  we  find  that  they 
are  frequently  more  capable  of  resisting  the  action 
of  the  denuding  agents  than  are  the  rocks  through 
which  they  have  broken,  especially  when  the 
denudation  is  largely  mechanical ;  in  these  circum- 
stances the  dykes  stand  out  as  ribs  of  rock,  looking 
like  walls  traversing  the  mountain  slope.  Anyone 
who  has  sailed  down  the  Clyde  and  passed  the  island 

LIBRARY 

•  Mji-.irnciTV    r\r   f»JU  ICHDlHt 


102     SCIENTIFIC   STUDY   OF   SCENERY 

of  Great  Cumbrae  must  have  noticed  two  remark- 
able wall -like  masses  of  rock  standing  out  above 
the  shore  near  Millport,  one  being  known  as  the 
Lion  Rock.  These  are  dykes  which  have  resisted 
denudation  to  a  greater  extent  than  the  surround- 
ing strata.  On  the  other  hand,  many  dykes  are 
more  prone  to  break  up  under  the  influence  of 
chemical  weathering  than  the  rocks  through  which 
they  are  intruded  ;  and,  instead  of  standing  out,  they 
give  rise  to  depressions  which  may  run  as  trenches 
along  comparatively  gentle  slopes  or  level  surfaces, 
or  form  couloirs  and  gullies  on  the  faces  of  steep 
slopes  and  precipices.  Several  gullies  on  the 
Scawfell  group  owe  their  existence  to  dykes  which 
have  been  thus  weathered.  When  weathering  ah>ng 
a  dyke  proceeds  to  a  sufficient  extent,  a  mountain 
peak  may  be  thus  severed  into  two,  with  a  deep 
gash  between,  an  event  which  has  occurred  on 
Scawfell.  The  highest  point,  Scawfell  Pike,  is 
separated  from  its  lower  neighbour,  Scawfell,  by  a 
deep  rent,  Mickledore,  which,  as  pointed  out  by 
the  late  Mr.  Clifton  Ward  many  years  ago,  is 
occupied  by  a  dyke  which  has  weathered  away 
more  rapidly  than  the  surrounding  rocks. 

The  characteristic  outlines  yielded  by  different 
forms  of  igneous  rocks  may  now  be  considered. 
Rocks  of  granitic  type  are  often  traversed  by  very 
regular  quadrangular  joints  which  give  rise  to  hemi- 
spherical and  pillow-shaped  outlines,  as  the  result  of 
the  action  of  the  weather,  for  a  reason  already  ex- 
plained when  describing  the  outlines  of  certain  hills, 
mainly  on  account  of  the  increased  action  of  the 
weather  at  the  edges  and  corners  of  the  masses. 
Accordingly  hills  composed  of  granitic  rocks  are 


MOUNTAINS  103 

often  dome-shaped  in  outline,  and  the  pillow  struc- 
ture is  characteristic  of  small  upstanding  masses, 
and  is  specially  emphasised  when  the  granite  forms 
"  tors,"  like  those  of  Devon  and  Cornwall.  Though 
this  is  the  normal  shape  of  granite  hills,  we  find  that 
many  granites  are  traversed  by  a  series  of  close-set 
parallel  joints,  which  give  rise  to  spiry  crests,  very 
different  from  the  ordinary  granitic  outlines,  as  seen 
in  the  case  of  the  granite  of  Arran,  rising  into  the 
sharp  crests  and  pinnacles  of  Goatfell,  that  of  the 
hills  surrounding  the  Bodethal,  near  Thale,  in  the 
Harz  mountains,  and  specially  in  that  type  of  granite 
known  as  protogine,  which  often  forms  the  cores  of 
Alpine  uplifts,  as,  for  instance,  in  the  Mont  Blanc 
massif. 

It  has  already  been  stated  that  the  basaltic  type 
of  rock,  when  occurring  on  a  large  scale,  is  prone  to 
occur  in  sheet-like  masses  of  wide  extent,  forming 
terraced  hills,  on  which  each  sheet  of  basalt,  usually 
well  divided  by  vertical  joints,  gives  rise  to  a  preci- 
pice. The  terraced  hills  of  many  of  the  western 
isles  of  Scotland,  of  parts  of  Greenland  and  other 
Arctic  islands,  of  the  Deccan  district  of  India,  and 
of  portions  of  the  western  territories  of  North 
America  are  of  this  character.  Another  feature 
which,  though  not  confined  to  basaltic  rocks,  is 
specially  frequent  in  them,  is  the  formation  of 
columnar  structure,  due  to  shrinking  of  the  mass 
while  cooling,  the  columns  usually  standing  at  right 
angles  to  the  cooling  surfaces.  I  need  only  refer 
to  the  Giant's  Causeway  and  Staffa  to  show  that  this 
columnar  structure  may  produce  locally  considerable 
effect  upon  the  scenery  of  a  district.  Another  feature 
often  found  in  basaltic  rocks  is  a  tendency  to  weather 


104    SCIENTIFIC   STUDY   OF   SCENERY 

into  exfoliating  spheroids,  which  often  occur  on  a 
considerable  scale. 

The  colour  of  granitic  rocks  is  often  sufficiently 
marked  to  influence  the  character  of  the  scenery. 
Many  of  them  are  of  a  prevailing  grey  hue,  owing 
to  the  admixture  of  white  felspar  with  dark  mica, 
while  if  the  felspar  is  pink,  a  distinct  pink  colour 
is  observable  at  a  distance.  The  basic  rocks  are 
often  dark,  sometimes  black,  and  as  the  result  of 
weathering  the  iron  silicates  contained  in  the  rocks 
are  converted  into  oxides  and  hydrates,  which  pro- 
duce the  rusty  oranges  and  browns  forming  so  marked 
a  feature  in  the  case  of  weathered  basic  rocks. 

Closely  connected  with  igneous  rocks  are  the  frag- 
mental  rocks  thrown  out  from  a  volcano.  These 
consist  of  particles  of  various  degrees  of  fineness, 
from  the  finest  dust  to  blocks  many  feet  in  diameter. 
These  volcanic  ashes,  when  incoherent,  allow  water 
to  percolate  through  them  with  ease,  and  are  apt  to 
retain  their  original  form.  Owing  to  their  composi- 
tion, they  may  be  converted  by  chemical  change  into 
rocks  of  extreme  hardness,  and  if  well  jointed,  give 
rise  to  rugged  eminences  and  precipices,  the  surfaces 
of  which  are  peculiarly  rough  owing  to  the  variation 
in  size  of  the  fragments  and  their  different  rates  of 
weathering.  The  precipices  of  Scawfell,  Great  Gable, 
and  other  hills  of  the  Lake  District  beloved  by 
climbers,  are  composed  of  altered  volcanic  ashes, 
and  to  their  texture  is  due  that  character  which 
renders  them  particularly  suitable  for  rock-climbing. 

The  group  of  rocks  to  which  the  term  "  crystalline 
schists "  is  applied  presents  many  points  of  resem- 
blance to  igneous  rocks,  and  indeed  many  of  the 
rocks  of  the  group  are  igneous  rocks  which  have 


MOUNTAINS  105 

undergone  alteration.  They  are  particularly  charac- 
terised by  the  possession  of  foliation  -  planes  (see 
Chapter  II.),  and  these  planes  are  frequently  curved 
in  a  very  remarkable  manner.  As  the  crystalline 
schists  are  usually  very  durable,  they  tend  to  resist 
denudation,  and  stand  out  as  mountain  ridges  and 
peaks.  Owing  to  the  closeness  of  the  foliation 
planes,  which  causes  the  weathered  rock  to  split 
into  thin  slabs,  the  crests  of  ridges  and  peaks  of 
hills  formed  of  schists  are  apt  to  be  extremely  jagged 
and  serrated  with  fragments  projecting  like  the  teeth 
of  a  saw,  and  as  the  planes  are  frequently  curved,  the 
pinnacles  and  teeth  frequently  present  curved  out- 
lines, recalling  in  many  cases  the  projecting  ribs  of  a 
wrecked  vessel. 

It  was  stated  in  Chapter  II.  that  slates  are  closely 
related  to  schists,  and  that  a  gradation  may  be  traced 
from  one  class  of  rock  to  the  other.  As  a  whole, 
slates  are  more  finely  crystalline  than  schists,  and  are 
more  readily  broken  up  by  the  action  of  the  weather. 
The  cleavage-planes  of  slates  are  more  close-set  and 
regular  than  those  of  schists,  so  that  when  slates  do 
stand  out  the  serrated  structure  of  a  ridge  may  be 
even  more  pronounced  than  that  of  a  roof  formed 
of  schists,  though  the  teeth  may  be  on  a  smaller 
scale. 

We  may  now  turn  to  the  consideration  of  the 
sedimentary  rocks,  which  for  our  purpose  may  be 
divided  into  sandstones,  shales,  and  limestones,  and 
discuss  the  scenic  effects  of  these  in  the  order 
mentioned. 

Sandstones  are  relatively  hard,  and  when  alternat- 
ing with  shales,  as  is  often  the  case,  tend  to  stand 
out,  while  the  shales  are  denuded.  The  joints  in 


io6     SCIENTIFIC   STUDY   OF   SCENERY 

sandstones  are  often  very  regular,  and  two  sets 
run  at  right  angles  to  the  planes  of  stratification  and 
to  one  another,  and  the  deposits  of  sandstone  fre- 
quently consist  of  beds  of  some  thickness,  the  im- 
portant bedding  planes  being  separated  from  one 
another  by  a  considerable  interval  of  rock.  Accord- 
ingly when  mountains  are  composed  of  horizontal 
or  nearly  horizontal  stratified  rocks  we  find  the 
sandstone  bands  marked  by  terraced  cliffs  and  scarps, 
so  well  described  by  Miss  Charlotte  Bronte  in  the 
case  of  the  characteristic  millstone  grit  scenery  of 
the  West  Riding  of  Yorkshire  around  her  native 
village.  Fig.  20  shows  a  diagrammatic  representa- 
tion of  a  hill  composed  of  alternate  deposits  of  nearly 
horizontal  sandstone  and  shale,  the  sandstone  being 
marked  by  dots  and  the  shale  by  fine  parallel  lines, 
and  a  similar  outline  would  be  produced  if  the  shale 
alternated  with  limestone  or  basalt. 

As  the  result  of  change,  sandstone  is  often  con- 
verted into  a  hard  white  rock,  quartzite,  which  is 
very  durable,  being  prone  to  resist  both  chemical 
and  mechanical  denudation,  and  accordingly  it  often 
gives  rise  to  eminences  which  frequently  betray  their 
character  owing  to  their  dazzling  whiteness.  Some 
of  the  quartzite-capped  hills  of  Sutherland  and  Ross, 
where  the  quartzite  reposes  upon  rocks  of  a  prevalent 
reddish  colour,  sometimes  appear  as  though  capped 
with  snow. 

The  upper  surfaces  of  gently  inclined  sandstones, 
often  laid  bare  to  form  gentle  slopes,  owing  to 
denudation  of  softer  beds  above,  may  simulate  to 
some  extent  the  surfaces  of  granitic  districts  and 
present  rounded  outlines,  though  very  frequently 
they  are  comparatively  flat  if  the  sandstone  is 


MOUNTAINS  107 

sufficiently  durable  to  resist  weathering  even  along 
joints.  The  effect  of  wind  on  masses  of  sandstone 
will  be  most  conveniently  considered  when  we  de- 
scribe the  characters  of  desert  regions. 

Shales  are  composed  of  very  fine  particles,  and  are 
generally  affected  by  close-set  planes  of  lamination. 
Jointing  is  also  often  on  a  smaller  scale  than  in  the 
case  of  sandstones,  and  as  the  result  of  weathering 
shales  tend  to  break  up  into  small  prismatic  frag- 
ments, which  present  many  surfaces  to  the  weather 
and  cause  the  rock  fragments  to  be  further  comminuted 
into  an  incoherent  mud,  which  is  readily  washed  to 
a  lower  level,  and  gives  rise  to  a  slope  of  loose 


FIG.  20. 

material  on  which  vegetation  will  readily  grow ; 
accordingly  shales  are  prone  to  produce  gentle 
grass-covered  slopes,  separating  the  cliffs  of  more 
durable  rock.  On  comparatively  level  surfaces, 
whether  on  the  mountain-side  or  the  lowlands, 
owing  to  the  impervious  nature  of  the  shale,  water 
finds  a  difficulty  in  penetrating  into  the  ground,  and 
in  humid  climates  a  tract  occupied  by  shales  is  apt 
to  give  rise  to  rushy  and  marshy  ground. 

The  peculiar  features  of  limestone  countries  are 
due  to  the  well-jointed  and  thick-bedded  character 
of  many  limestones,  and  to  their  porosity  and  solu- 
bility. The  rocks  break  along  joint-planes,  producing 
cliffs  resembling  those  formed  by  sandstones.  As 
limestone  is  fairly  soluble  in  carbonated  water,  and 


io8     SCIENTIFIC   STUDY   OF   SCENERY 

as  solution  occurs  along  the  joint-planes  more  ex- 
tensively than  elsewhere,  much  of  the  drainage  of 
limestone  is  underground,  giving  rise  to  caves,  whose 
structure  will  be  considered  elsewhere.  Owing  to 
this  underground  drainage,  limestones  are  often 
marked  by  absence  of  surface  streams,  and  corrasion 
is  of  little  account,  and  accordingly  even  soft  lime- 
stones like  chalk  often  stand  out  as  hills.  As  the 
rain  penetrates  along  joint-planes  the  limestone  is 
often  cut  up  into  more  or  less  quadrangular  columns 
and  pinnacles,  and,  owing  to  solution  along  fairly 
horizontal  bedding  planes,  these  pinnacles  become 
fretted  in  an  extraordinary  manner.  The  small 
hollows  on  the  general  surface  of  a  fairly  horizontal 
tract  of  limestone  hold  the  water,  and  solution  takes 
place  in  these  hollows,  causing  their  gradual  enlarge- 
ment. Accordingly  the  surfaces  of  fairly  level  lime- 
stone tracts  (known  as  "  clints "  in  the  north  of 
England)  present  a  rough,  irregular  surface,  tra- 
versed by  wide  open  fissures  penetrating  to  a 
considerable  depth,  often  filled  by  masses  of  harts- 
tongue  and  other  ferns,  while  the  surface  of  the 
limestone  is  apt  to  be  bare  of  vegetation,  or  if  the 
limestone  is  impure  a  thin,  dry  soil  is  formed,  which 
gives  rise  to  a  short,  sweet  herbage  like  that  covering 
the  chalk  downs. 

The  characters  of  a  limestone  area  are  often 
developed  in  an  exaggerated  form  in  a  region  com- 
posed of  the  rock  formed  of  carbonates  of  lime  and 
magnesia,  and  usually  spoken  of  as  dolomite.  The 
joints  in  this  rock  are  frequently  developed  with 
extraordinary  regularity,  and  give  rise  to  those  re- 
markable mural  precipices  and  pinnacles  which  have 
caused  a  certain  area  of  the  Eastern  Alps  to  be 


PHE    DREI    ZINNEN 


MOUNTAINS  109 

spoken  of  by  the  title  of  "The  Dolomite  Mountains." 
The  Drei  Zinnen  (shown  in  the  plate)  and  the 
Fiinffingerspitze  are  well-known  examples  of  this 
structure.  Solution  along  bedding  and  joint-planes 
also  produces  very  characteristic  effects  in  detail, 
many  of  the  summit  ridges  of  the  dolomite  districts 
resembling  piles  of  ruined  masonry.  The  charac- 
teristic outline  of  dolomite  rock,  though  specially 
well  shown  in  the  Eastern  Alps  on  a  large  scale,  is 
frequently  reproduced  on  a  small  scale  among  the 
masses  of  dolomite  which  occur  here  and  there 
among  the  crystalline  rocks  of  the  Valais  and  other 
parts  of  Western  Switzerland. 

Before  leaving  the  present  subject  reference  must 
be  made  to  the  quartz  veins  which  frequently  traverse 
rocks  of  many  kinds,  both  aqueous  and  igneous. 
They  have  been  deposited  from  solution  along  the 
various  planes  of  weakness  which  traverse  the  rocks, 
and  occur  sometimes  in  regular  bands,  at  other 
times  in  an  irregular  interlacing  network  of  strings 
and  knots.  They  frequently  produce  an  effect 
owing  to  their  conspicuous  whiteness,  but  are  also 
important  to  us  because  they  often  furnish  a  hard 
skeleton  to  rocks  which  are  otherwise  soft,  causing 
them  to  resist  denudation  and  to  stand  out  as 
hills. 

Passing  from  the  influence  of  particular  kinds  of 
rocks  upon  scenery,  we  must  still  say  something  about 
major  divisional  planes  which  traverse  great  belts  of 
rock  of  diverse  composition,  and  also  concerning  the 
alternation  of  inclined  rocks  of  different  degrees  of 
hardness.  Divisional  planes,  such  as  faults  or  parallel 
systems  of  faults,  act  as  planes  of  weakness  along 
which  denudation  readily  acts,  and  the  same  may 


i  io     SCIENTIFIC    STUDY   OF   SCENERY 

be  said  of  inclined  soft  strata.  Complications  thus 
arise  in  the  drainage  lines  which  modify  to  a 
considerable  degree  the  initial  drainage  which  was 
established  in  accordance  with  the  laws  which  we 
have  discussed.  These  complications  will  be  more 
fully  considered  when  we  treat  of  the  formation  of 
valleys  in  greater  detail,  and  they  are  referred  to 
here  in  order  to  point  out  their  effect  upon  moun- 
tains. We  have  seen  that  mountain  peaks  are 
normally  formed  along  ridges,  and  that  each  moun- 
tain peak  of  a  symmetrical  mountain  ridge  is 
separated  from  adjoining  peaks  by  cols,  and  stands 
at  the  head  of  a  consequent  valley,  while  a  secondary 
ridge  extends  in  a  direction  opposite  to  that  of 
the  valley.  Accordingly  most  mountain  peaks 
are  merely  the  culminating  points  of  ridges,  with 
a  long  slope  facing  the  consequent  valley,  and  two 
aretes,  or  ridges,  stretching  to  the  cols.  A  true 
pyramid  is  therefore  rare,  and  when  it  occurs  excites 
interest.  If  in  any  way  the  ridge  which  extends 
from  a  peak  in  a  direction  opposite  to  the  conse- 
vquent  valley  is  cut  through,  the  peak  may  become 
a  true  pyramid.  On  the  flanks  of  the  Pennine 
chain,  in  its  course  through  Westmorland,  four 
great  buttresses — Roman  Fell,  Murton  Pike,  Dufton 
Pike,  and  Knock  Pike — stand  out  from  the  escarp- 
ment. Two  of  these,  Murton  and  Dufton  Pikes, 
are  true  pyramids,  and  form  very  conspicuous  objects 
from  the  main  line  of  the  Midland  Railway.  They 
were  once  the  terminations  of  secondary  ridges, 
coming  from  the  Pennines  ;  but  owing  to  the 
existence  of  a  fault  between  them  and  the  main 
scarp  of  the  Pennines,  denudation  has  occurred 
along  the  plane  of  weakness,  producing  a  depression, 


MOUNTAINS  in 

which  has  caused  the  Pikes  to  stand  out  as 
pyramids. 

Still  more  striking  is  the  case  of  the  Matterhorn, 
that  mysterious-looking  pyramid  which  has  excited 
the  wonder  of  all  who  have  gazed  at  its  apparently 
unscaleable  cliffs.  It  has  already  been  pointed  out 
that  it  occurs  at  the  head  of  the  Val  Tournanche, 
and  is  separated  from  the  Breithorn  on  one  side 
and  the  Dent  d'Herens  on  the  other  by  cols,  and 
that  a  secondary  ridge  once  extended  from  it  on 
which  the  Weisshorn  stands.  This  secondary  ridge 
has  been  cut  through  by  the  valley  occupied  by 
the  Zmutt  glacier,  which  owes  its  existence  to  a 
line  of  weakness  apparently  due  to  the  occurrence 
of  a  belt  of  comparatively  soft  rock,  which  extends 
across  the  Zermatt  valley  beneath  the  valley 
occupied  by  the  Findelen  glacier.  Accordingly  we 
find  the  Matterhorn,  formerly  the  end  of  a  long 
ridge  at  its  junction  with  the  main  ridge,  now 
approaching  the  form  of  a  true  pyramid.  (See  the 
plate.) 

Vegetation  on  Mountains, — It  is  well  known  that 
elevation  produces  its  effect  upon  the  character  of 
the  vegetation,  and  that  a  mountain  near  the  equator 
rising  to  the  snow  line  is  occupied  by  zones  of  vegeta- 
tion which,  to  some  extent,  represent  the  zones  which 
are  traceable  when  travelling  from  equatorial  to  polar 
regions.  The  detailed  changes  in  vegetation  vary 
with  the  geographical  position  of  the  mountains,  but 
whereas  the  lower  slopes  of  the  mountains  in  all 
but  arctic  regions  are  frequently  covered  by  belts 
of  dense  forest,  these  are  replaced  higher  up  by 
shrubby  growths,  still  higher  by  grassy  slopes  en- 
riched by  numerous  brilliantly  coloured  flowering 


ii2     SCIENTIFIC   STUDY   OF   SCENERY 

plants,  at  a  higher  elevation  by  lichens,  and  at  last 
by  bare  rock  or  perpetual  snow.  The  peculiar  type 
of  vegetation  which  constitutes  what  is  known  as 
an  Alpine  flora  exerts  considerable  influence  upon 
the  scenery  owing  to  the  peculiar  conditions  under 
which  it  grows.  Supplied  with  abundance  of  water 
during  the  times  of  melting  snow,  and  at  other  times 
deprived  of  an  outward  supply  of  water  during  long 
intervals,  the  growth  of  the  plants  is  modified  in 
various  ways  to  meet  the  peculiar  conditions. 
Specially  interesting  to  us  is  the  formation  of  the 
cushion-shaped  masses  of  plants,  often  covered  with 
a  profusion  of  bright  flowers.  As  in  the  case  of 
species  of  Silene,  Androsace,  Petrocallis,  and  Eritri- 
chium,  these  masses  frequently  occur  in  such  abun- 
dance on  rocky  slopes  and  moraines,  that  they  pro- 
duce a  very  marked  and  pleasing  influence  upon  the 
character  of  the  scenery. 


CHAPTER    IX. 

VALLEYS 

VALLEYS  are  of  two  kinds,  namely,  those  pro- 
duced by  earth  movement  and  those  produced 
by  denudation,  though  as  in  the  case  of  mountains, 
so  in  that  of  valleys,  the  two  processes  work  together. 
As  the  ridge  of  an  earth-wave  produces  a  mountain 
range,  so  the  trough  gives  rise  to  a  valley  of  de- 
pression, and  when  mountains  are  sculptured  by 
denuding  agents  the  intervening  gaps  are  left  as 
valleys  of  denudation. 

Valleys  of  depression  will  coincide  with  troughs  of 
the  strata,  or  we  may  have  one  side  of  the  valley 
defined  by  a  fault  which  replaces  the  septum  of  the 
earth-wave. 

Of  valleys  which  are  primarily  defined  by  folding, 
we  may  mention  in  our  own  country  the  lower  part 
of  the  Thames,  between  Windsor  and  the  sea,  while 
abroad  a  good  instance  is  furnished  by  the  upper  part 
of  the  Rhone  valley,  between  its  source  and  Martigny, 
separating  the  Alps  of  the  Bernese  Oberland  from  those 
of  the  Valais.  In  each  case  the  river  runs  along  the 
bottom  of  a  trough-shaped  fold.  An  example  of  a 
valley  produced  by  a  faulted  depression  is  that  part 
of  the  Vale  of  Eden  which  lies  between  Kirkby 
Stephen  and  Carlisle,  and  an  admirable  example  on  a 
large  scale  in  a  foreign  country  is  supplied  by  the 
Jordan  valley,  and  its  prolongation  to  the  southward, 
i  "3 


ii4    SCIENTIFIC   STUDY   OF   SCENERY 

Though  geologists  are  generally  agreed  that  the 
majority  of  valleys  are  formed  by  erosion,  and  not 
by  folding  or  cracking  of  the  earth's  crust,  there  are 
many  people  who  will  feel  surprised  when  told  that 
a  river  can  carve  out  its  own  valley.  Anyone  who 
carefully  considers  the  laws  of  erosion,  as  described 
in  the  preceding  chapters  on  mountains,  and  sees 
how  exactly  the  directions  and  structures  of  valleys 
of  erosion  agree  with  those  which  they  should  possess 
in  accordance  with  those  laws,  will,  I  think,  be  com- 
pelled to  admit  that  these  valleys  must  have  been 
carved  by  erosion,  but  it  will  perhaps  be  as  well 
to  give  some  evidence  that  rivers  can  and  do  erode 
their  valleys,  though  we  cannot  afford  space  to  treat 
the  matter  at  great  length. 

In  the  first  place,  it  may  be  remarked  that  many 
people  have  a  very  exaggerated  notion  of  the  slopes 
of  valleys  and  mountains.  Writers  talk  glibly  of 
precipices  and  beetling  cliffs  when  the  prosaic  sur- 
veyor finds  that  the  general  slope  is  perhaps  less 
than  45°.  Vertical  precipices  on  a  large  scale  are 
very  rare,  and,  as  before  remarked,  form  comparatively 
insignificant  features  on  a  mountain-side  when  the 
mountain  is  viewed  from  a  distance.  Mr.  Whymper 
notes  that  the  east  face  of  the  Matterhorn,  which  looks 
so  steep  when  viewed  from  the  Riffel,  slopes  at  an 
angle  scarcely  exceeding  40°,  and  he  remarks  : — 

"  Forty  degrees  may  not  seem  a  formidable  inclination  to 
the  reader,  nor  is  it  for  only  a  small  cliff.  But  it  is  very 
unusual  to  find  so  steep  a  gradient  maintained  continuously 
as  the  general  angle  of  a  great  mountain  slope,  and  very 
few  instances  can  be  quoted  from  the  High  Alps  of  such  an 
angle  being  preserved  over  a  rise  of  3000  feet."1 

1  WHYMPER,  E.,  The  Ascent  of  the  Matterhorn,  p.  228. 


VALLEYS  115 

On  the  accompanying  figure  (Fig.  21  B)  is 
shown  a  section  through  Mont  Blanc  and  the 
valleys  of  Chamonix  and  of  the  river  Doire,  which 
is  a  portion  of  a  section  having  the  same  vertical 
and  horizontal  scale  given  by  the  late  Sir  H.  de  la 
Beche  in  Plate  II.  of  his  Sections  and  Views  Illus- 
trative of  Geological  Phenomena,  while  above  it  (A} 
is  a  section  across  Snowdon  reduced  from  one  of 
the  horizontal  sections  of  H.M.  Geological  Survey  on 


Srwwdan 


FIG.  21. 
A  =  Section  across  Snowdon  from  Llanberis  to  Gwynant.  (Ajter  Sir 

A.  RAMSAY.) 

B  =  Section  across  Mont  Blanc.  (After  Sir  H.  DE  LA  BECHE.) 

In   each   section   the   Vertical  scale  is   the  same  as   the  horizontal 

scale.     The  scale  of  Section  A  is  about  three  times  as  great  as  that  of 

Section  B. 

the  scale  of  six  inches  to  the  mile,  horizontal  and 
vertical.  These  are  sufficient  to  show  the  compara- 
tive smallness  of  angles  in  slopes  which  appear  to  be 
very  steep. 

Examination  of  sections  across  valleys  drawn  to 
true  scale  will  convince  anyone  that  the  majority 
of  valleys  are  not  mere  cracks  produced  by  fissuring 
of  the  earth's  crust.  It  has  already  been  stated  that 
some  valleys  of  depression  are  determined  by  lines 
of  fault  (though  it  can  generally  be  proved  that  even 


ii6     SCIENTIFIC   STUDY   OF   SCENERY 

these  largely  owe  their  present  features  to  subsequent 
denudation),  but  as  it  is  found  that  most  valley 
bottoms  are  not  occupied  by  faults,  but  that  the 
rock  runs  unbroken  across  them,  faulting  is  out  of 
the  question  in  those  cases.  Again,  it  might  be 
supposed  that  valleys  could  be  produced  by  bending 
of  the  strata  into  an  arch  which  was  ruptured  at  the 
summit,  giving  rise  to  a  V-shaped  opening,  and  the 
coincidence  of  many  valleys  with  lines  of  anticlinal 
folds  of  the  strata  seems  at  first  sight  to  countenance 
this  view.  On  examination,  however,  it  is  usually 
found  that  the  slope  of  the  strata  is  much  smaller 
than  it  should  be  if  this  were  the  explanation  of 
the  origin  of  valleys.  If  a  valley  were  formed  by 
rupture  of  an  arch  composed  of  strata  which  were 
originally  horizontal,  and  the  rupture  gaped  to  such 
an  extent  as  to  give  the  valley  sides  slopes  of  30°, 
a  slope  which  is  above  the  average  slope  of  valleys, 
the  strata  should  dip  away  at  an  angle  of  60°  on 
either  side,  whereas  when  the  direction  of  a  valley 
does  coincide  with  that  of  the  axis  of  an  anticlinal 
fold  the  dip  of  the  strata  on  either  side  is  often  quite 
gentle.  There  is  one  method  of  producing  an  open 
depression  by  earth  movement  which  has  perhaps 
not  received  the  attention  which  it  deserves.  When 
an  arch  is  formed  the  upper  strata  are  bent  into 
a  larger  curve  than  the  lower  ones,  and  cracks  may 
be  formed  in  the  upper  beds  which  do  not  extend 
to  the  lower  ones ;  furthermore  lateral  sliding  of  the 
upper  strata  along  a  well-marked  plane  of  stratifica- 
tion may  take  place,  thus  giving  rise  to  a  depression 
bounded  by  heights  on  either  side.  In  rocks  which 
have  been  subjected  to  much  folding,  it  is  probable 
that  minor  valleys  have  often  been  initiated  in  this 


VALLEYS  117 

way,  but  as  a  general  rule  we  have  abundant  evidence 
that  the  action  has  not  been  responsible  for  the 
formation  of  valleys.  It  may  be  further  remarked 
that  the  slope  of  a  valley  formed  in  this  way  should 
approach  a  plane  surface,  whereas  the  sides  of  valleys 
in  regions  which  are  marked  by  copious  rainfall  have 
the  curve  characteristic  of  stream  erosion. 

Anyone  taking  his  stand  on  a  height  overlooking 
one  of  the  Yorkshire  dales,  say  the  slopes  of 
Ingleborough,  will  see  the  nearly  horizontal  escarp- 
ments of  the  harder  strata  sweeping  in  continuous 
curves  round  the  sides  and  heads  of  the  valleys, 
each  major  deposit  obviously  represented  by  the 
corresponding  strata  on  the  other  side  of  the  valley, 
and  examination  of  such  a  scene  will  be  more  useful 
than  pages  of  description  devoted  to  the  subject  to 
convince  an  observer  that  the  valley  has  been  carved 
out  by  erosion. 

But  hitherto  we  have  only  put  forward  indirect 
proofs  that  running  water  can  erode.  We  have 
discussed  the  ideal  curve  of  stream  erosion,  and  seen 
that  the  actual  curve  corresponds  with  it  in  areas 
where  streams  course  over  the  surface  of  the  country, 
and  that  the  curves  are  absent  where  streams  are 
wanting.  Let  us  now  examine  the  action  of  these 
streams,  in  order  to  see  whether  they  are  capable 
of  exerting  the  requisite  erosive  power,  for  many 
writers,  though  admitting  a  limited  erosive  power 
to  rivers,  deny  that  these  are  capable  of  performing 
the  work  which  geologists  claim  for  them,  and  this 
is  not  to  be  wondered  at,  when  the  chances  are  that 
the  first  river  which  is  examined  will,  under  existing 
conditions,  have  reached  its  base-level  of  erosion  in 
a  country  which  has  not  recently  uprisen. 


ii8     SCIENTIFIC   STUDY   OF   SCENERY 

If  we  take  our  stand  by  the  side  of  a  small  rocky 
gorge,  we  shall  probably  see  a  number  of  hemi- 
spherical or  cylindrical  hollows  in  the  bed  of  the 
stream  and  semi  -  cylindrical  shafts  on  the  rocky 
walls,  which  are  known  as  potholes.  Those  which 
are  submerged,  as  well  as  those  which  are  now  high 
and  dry,  will  probably  be  occupied  by  a  number  of 
water-worn  pebbles.  During  a  flood  it  will  be  seen 
that  eddies  are  at  work  over  these  hollows,  and  that 
the  pebbles  are  whirled  round  and  round  by  the 
eddies,  gradually  boring  their  way  into  the  rock,  like 
the  drill  of  a  diamond  boring  machine.  In  time  two 
contiguous  potholes  join,  and  so  a  whole  number 
may  coalesce,  and  by  their  coalescence  the  gorge  is 
deepened,  and  some  of  the  isolated  potholes  left  dry 
above  the  existing  stream-level.  In  this  case  it  is 
seen  how  a  gorge  can  be  formed,  and  its  size  is 
merely  a  question  of  time,  so  long  as  the  stream 
can  work  without  reaching  its  base-level  of  erosion. 
Now  take  the  case  of  a  gorge  below  a  waterfall,  as, 
for  instance,  Niagara.  We  know,  as  the  result  of 
direct  observation,  that  the  falls  are  cutting  back- 
ward;  and  we  also  know  that  the  structure  of  the 
gorge  is  essentially  similar  through  the  whole  of  its 
extent,  and  accordingly  writers  are  agreed  that 
Niagara  has  cut  out  a  gorge  from  200  to  400  yards 
wide  at  the  top,  200  to  300  feet  deep,  and  seven 
miles  in  length,  in  times  which  are,  in  a  geological 
sense,  recent.1  Here  is  a  gorge  which,  it  is  generally 
admitted,  has  been  carved  by  the  river  which  now 
occupies  it.  But  we  find  every  gradation  from  the 
waterfall,  through  the  cascade  and  the  rapids,  to  the 

1  For  a  full  account  of  the  formation  of  the  Niagara  gorge,  see 
LYELL,  Sir  C.,  Principles  of  Geology,  nth  edition,  vol.  i.,  chap.  xv. 


VALLEYS  119 

ordinary  flowing  river.  The  work  is  performed  in 
each  case  in  the  same  way,  it  is  only  the  amount 
which  is  different;  this  amount,  as  we  have  seen, 
being  dependent  on  declivity,  when  other  things  are 
equal.  We  may  cite  a  few  other  instances  of  actual 
formation  of  small  valleys  which  are  known  to  have 
been  formed  by  water  action.  "A  great  mass  of 
debris  was  washed  down  from  the  sides  of  Blease 
Fell,  on  the  east  of  the  Lune,  about  two  miles  south 
of  Tebay  Junction,  in  the  course  of  three  or  four 
hours  during  a  thunderstorm,  about  the  year  1858. 
The  rain  excavated  deep  channels  in  the  weathered 
rock  of  the  hill-side,  and  spread  the  rubbish  over 
some  pasture  land  below.  The  debris  still  forms  a 
striking  object  as  seen  from  the  train."1  Gilpin2 
describes  the  occurrence  of  a  "cloud-burst"  in  the 
Vale  of  St.  John,  in  the  Lake  District,  on  August 
22nd,  1/49,  "which  forced  a  new  channel  through 
a  solid  rock  .  .  .  and  made  a  chasm  at  least  ten  feet 
wide."  Again,  in  the  same  district,  "an  interesting 
gully  is  seen  somewhat  north  of  the  top  of  High 
Street,  where,  as  seen  on  the  six-inch  ordnance  map, 
the  Roman  road  is  partially  destroyed  by  a  ravine, 
which  has  cut  through  it.  The  head  of  the  ravine 
is  a  few  yards  above  the  road,  and  where  it  cuts  the 
road  it  is  about  eighteen  feet  deep  and  103  feet  across 
at  the  top.  It  is  excavated  partly  in  loose  rubble, 
but  largely  through  rock  in  situ,  though  much 
affected  by  weathering.  Some  of  the  material  may 
have  been  removed  by  landslip,  but  the  greater  part 

1  STRAHAN,  A.,  Mem,  Geol.  Survey,  "The  Geology  of  the  District 
around  Kendal,"  etc.,  p.  51. 

2  Observations  on   the  Mountains   and  Lakes  of  Cumberland  and 
Westmorland,  vol.  ii.,  p.  36. 


120    SCIENTIFIC    STUDY    OF   SCENERY 

was  probably  disintegrated  by  running  water,  which 
has  also  removed  it."1  In  Lyell's  Principles  of 
Geology  (vol.  i.,  chap,  xv.)  an  example  is  given  of  a 
gorge  "  from  fifty  to  several  hundred  feet  wide,  and 
in  some  parts  from  forty  to  fifty  feet  deep,"  which 
has  been  excavated  by  the  river  Simeto  in  a  current 
of  lava  which,  according  to  Gemmellaro,  flowed  from 
Etna  in  1603.  "On  entering  the  narrow  ravine 
where  the  water  foams  down  the  two  cataracts,  we 
are  entirely  shut  out  from  all  view  of  the  surround- 
ing country,  and  a  geologist  who  is  accustomed  to 
associate  the  characteristic  features  of  the  landscape 
with  the  relative  age  of  certain  rocks  can  scarcely 
dissuade  himself  from  the  belief  that  he  is  contem- 
plating a  scene  in  some  rocky  gorge  of  very  ancient 
date." 

These  examples  will  suffice  to  show  that  rivers 
can  erode,  and  the  last  is  specially  instructive.  If 
a  gorge  forty  to  fifty  feet  deep  can  be  carved  out 
of  hard  rock  in  less  than  three  centuries,  how  much 
greater  effects  can  be  produced  during  the  vast 
intervals  of  time  which  we  can  prove  to  have  elapsed 
since  the  initiation  of  many  of  our  existing  drainage 
systems. 

In  some  of  the  examples  cited,  it  will  be  noted 
that  the  work  was  done  during  periods  of  excessive 
rainfall,  and  it  must  be  remarked  that  periods  of 
flood  are  the  times  when  the  work  of  denudation  is 
almost  exclusively  performed.  The  transporting 
power  of  a  river  varies,  not  directly  as  the  velocity, 
but  as  the  sixth  power  of  the  velocity,  and  accord- 
ingly the  corrasive  power  of  a  river  is  enormously 
increased  during  periods  of  flood.  This  should  be 

1  Geographical  Journal,  Tune,  1895,  p.  621. 


VALLEYS  121 

remembered  by  those  who  are  inclined  to  minimise 
the  importance  of  rivers  as  agents  of  denudation. 
In  the  forty  years  that  have  elapsed  since  the  for- 
mation of  the  ravines  on  Blease  Fell,  near  Tebay, 
the  erosion  which  has  occurred  is  as  nothing  com- 
pared with  that  which  was  then  performed  in  a  few 
hours. 

In  Chapter  V.  allusion  was  made  to  the  initiation 
of  the  chief  drainage  lines  of  a  country  which  had 
undergone  uplift,  producing  a  set  of  primary 
consequent  streams  running  in  a  general  direction 
at  right  angles  to  the  axis  of  uplift,  and  therefore 
along  the  direction  of  the  dip  of  the  beds,  and 
another  set  of  secondary  subsequent  streams  whose 
courses  are  directed  along  the  strike  of  the  strata, 
and  approximately  at  right  angles  to  those  of  the 
consequent  streams.1  We  have  stated  that  the  con- 
sequent and  subsequent  streams  would,  if  conditions 
were  uniform,  run  in  straight  lines,  and  the  main 
direction  of  these  streams  often  approaches  the 
straight  line,  but  in  uplift  of  actual  rocks  thousands 
of  minor  inequalities  would  occur  which  would  divert 
the  stream  now  on  one  side,  now  on  another,  from 
its  ideal  course,  and  give  it  a  sinuous  track.  The 
subsequent  streams  will  only  be  approximately  at 
right  angles  to  the  consequent  streams,  for  although 
the  secondary  watershed  between  neighbouring  con- 
sequent streams  is  parallel  to  the  courses  of  those 
streams,  the  subsequent  streams  are  also  affected  by 
the  general  declivity  of  the  land  towards  the  ocean, 

1  The  terms  "consequent"  and  "subsequent"  are  applied  to  rivers 
by  Professor  W.  M.  Davis  in  a  paper  on  "The  Development  of  Certain 
English  Rivers"  (Geograph.  Journal,  vol.  v.,  p.  127),  which  very 
clearly  describes  the  initiation  of  a  typical  drainage  system  and  its 
changes. 


122     SCIENTIFIC   STUDY   OF  SCENERY 

and  though  this  will  probably  be  slight  as  compared 
with  the  slope  between  the  secondary  watershed  and 
the  bottom  of  the  consequent  valley,  it  will  produce 
its  effect,  and  cause  the  subsequent  streams  to  run 
somewhat  obliquely  to  the  strike  of  the  strata  on 
their  way  to  join  the  consequent  streams. 

Consequent  streams,  being  in  the  direction  of  the 
dip,  have  the  divisional  planes  of  the  rocks  on  either 
side  of  the  stream  bearing  the  same  relations  to  the 
stream  if  conditions  be  uniform,  but  this  is  not  the 
case  with  subsequent  streams,  and  accordingly  the 
cross-section  of  a  subsequent  stream  is  apt  to  be 
unsymmetrical.  In  an  ideal  uplift  the  subsequent 
stream  will  at  first  run  over  one  stratum,  the  upper- 
most, but,  its  course  being  somewhat  oblique,  it  will 
flow  over  different  strata  as  it  corrades  its  valley; 
though,  as  shown  by  Gilbert,  in  a  region  of  inclined 
strata  there  is  a  tendency  on  the  part  of  streams 
which  traverse  soft  beds  to  continue  therein,  and 
there  is  a  tendency  to  eliminate  drainage  lines  from 
hard  beds. 

In  Fig.  22  let  A  B  be  the  surface  of  the  ground,  on 
which  a  series  of  inclined  strata,  H  S,  crop  out,  and 
let  H  be  hard  and  S  soft  strata.  Suppose  a  sub- 
sequent stream  running  on  a  hard  stratum  at  X,  the 
cross-section  of  its  valley  at  the  outset  being 
indicated  by  the  semicircular  unbroken  line.  The 
stream,  if  the  hard  rock  be  uniform,  will  corrade 
vertically  downward  till  it  reaches  the  softer  rock 
below,  and  if  this  be  also  uniform,  it  will  corrade 
downward  through  this  also,  as  shown  by  the  loop- 
shaped  dotted  lines  marking  different  stages  of  its 
progress.  When  it  reaches  the  underlying  hard 
stratum  it  will  probably  find  it  easier  to  cut  sideways 


VALLEYS  123 

along  the  junction  of  soft  and  hard  strata,  as  shown 
by  the  dotted  lines  to  the  right  of  the  position  of  the 
original  stream,  and  will  tend  to  undercut  the  over- 
lying hard  stratum.  At  Y,  where  the  stream  is 
supposed  to  originate  in  the  soft  rock,  it  cuts 
vertically  down  to  the  junction  with  the  underlying 
hard  rock,  and  then  cuts  sideways  as  before,  and  a 
stream  developed  along  the  soft  rock  between  X 
and  Y  would  act  similarly.  Now  we  have  seen 
(Chapter  II.)  that  the  master-joints  of  rocks  run  in 
two  sets,  respectively  parallel  with  the  lines  of  dip 
and  strike,  and  as  the  overlying  hard  rocks  are 


X 


FIG.  22. 

undercut  they  will  be  detached  by  the  action  of  the 
weather  and  in  landslips,  and  the  material  will  fall 
into  the  stream  and  be  transported.  In  gently 
inclined  rocks  the  joints  will  be  highly  inclined,  and 
accordingly  every  valley  formed  by  a  subsequent 
stream  will,  when  the  inclination  of  the  strata  is  less 
than  45 °,  as  is  usually  the  case,  have  a  gentle  slope 
on  one  side,  formed  by  the  summit  of  a  hard  rock 
(and  this  slope  will  possess  the  direction  and  degree 
of  inclination  of  the  dip  of  the  rock),  and  a  steep 
slope  on  the  other,  corresponding  with  the  inclination 
of  the  strike  joints.  Accordingly,  after  gently 
inclined  rocks  are  affected  by  the  corrasion  of 
subsequent  streams,  a  section  across  the  country  at 
right  angles  to  the  direction  of  flow  of  the  sub- 
sequent streams  will  present  the  appearance  shown 


i24     SCIENTIFIC   STUDY   OF   SCENERY 

in  Fig.  23.  The  gentle  slopes,  D,  are  known  as  dip- 
slopes,  and  the  steeper  ones,  E,  as  escarpments,  and 
every  escarpment  in  a  district  which  has  been  formed 
by  a  simple  uplift  of  strata  above  sea-level  will  face 
inland,  and  each  dip-slope  will  slant  down  seaward. 
In  many  cases,  especially  with  softer  rock,  the  slope 
of  the  escarpment,  and  often  the  dip  slope  also,  will 
be  diminished  by  accumulation  of  loose  material,  but 
with  hard  rocks  the  escarpments  often  stand  out 
as  parallel  lines  of  cliff,  each  cliff  being  limited  to 
the  hard  stratum  or  set  of  strata  to  which  it  owes  its 
origin.  These  escarpments,  of  course,  give  rise  to 
tertiary  watersheds,  from  which  streams  flow  in 


either  direction.  Those  which  flow  down  the 
escarpment  in  a  direction  contrary  to  that  of  the 
primary  consequent  streams  are  termed  obsequent 
streams  by  Professor  Davis  ;  the  other  streams  which 
flow  down  the  dip-slopes  will  have  courses  parallel  to 
those  of  the  primary  consequent  streams. 

When  we  meet  with  great  belts  of  alternating 
soft  and  hard  strata,  the  escarpments  may  recede 
owing  to  general  degradation  by  weathering  and 
the  action  of  obsequent  streams  and  their  tribu- 
taries, and  the  escarpment  may  recede  while  the 
subsequent  stream  which  determines  it  remains 
practically  stationary ;  we  then  get  an  extensive 
plain  occupied  by  the  subsequent  stream  and 
its  tributaries,  and  the  courses  of  obsequent 


VALLEYS  125 

streams  are  lengthened  by  recession  of  the  top 
of  the  escarpment.  Thus  we  find  the  great  plain 
of  the  soft  lias  and  new  red  sandstone  rocks  of 
the  east  and  south-east  of  England  dominated  by 
the  westward-facing  escarpment  of  the  hard  oolites. 
Approaching  the  east  coast,  we  find  that  the  dip- 
slope  of  the  oolites,  sloping  eastward,  plunges  down 
to  another  plain  formed  of  the  soft  upper  Jurassic 
clays.  Another  escarpment  facing  westward  is  fre- 
quently encountered,  formed  of  the  more  durable 
lower  greensand,  the  dip -slope  of  which  in  turn 
sinks  to  the  plain  of  soft  gault  clay,  which  is  over- 
looked by  the  great  escarpment  of  chalk,  again 
facing  westward.  These  two  salient  escarpments, 
that  of  the  oolites  and  that  of  the  chalk,  with  their 
corresponding  plains,  formed  in  the  way  described 
above,  form  dominant  features  of  the  scenery  of  the 
south-east  portion  of  England. 

Owing  to  the. tendency  of  the  streams  which  run 
obliquely  across  harder  and  softer  strata  to  eliminate 
their  courses  from  the  harder  rocks,  and  to  flow 
when  possible  over  soft  strata,  a  subsequent  stream 
with  an  oblique  course,  indicated  by  the  dotted  line 
in  the  following  plan,  in  which  the  outcrops  of  hard 
and  soft  strata  are  respectively  represented  by  the 
letters  H  and  S,  will  tend  to  alter  its  course,  so 
that  it  ultimately  flows  in  the  direction  indicated  by 
the  thick  black  line,  though  it  must  be  understood 
that  the  stream,  with  its  altered  course,  would  not  be 
actually  beneath  the  original  one,  as  the  whole  has 
shifted  laterally.  (The  arrow  indicates  the  direction 
of  dip  of  the  strata.) 

The  formation  of  obsequent  streams,  and  of  the 
other  tributaries  to  a  subsequent  stream  which  run 


126     SCIENTIFIC   STUDY   OF   SCENERY 

down  the  dip-slopes,  will  give  rise  to  another  set  of 
watersheds  from  which  subsidiary  tributaries  may 
flow,  so  that  a  river  system  eventually  may  consist  of 
consequent  stream,  with  a  whole  network  of  tributaries, 
but  with  the  formation  of  subsequent  streams  and 
their  main  tributaries  we  have  obtained  a  sufficient 
insight  into  the  development  of  a  typical  drainage 
system  in  an  area  affected  by  a  symmetrical  uplift. 

Before  considering  the  deviations  of  drainage 
which  may  be  subsequently  produced  in  different 
ways  in  an  uplifted  area,  it  will  be  convenient  if 


H 


s                      ~ZL     J 

jj 

^'1 

s 

/       t 

ff     .--- 

FIG.  24. 

we   devote   a   short   space   to   consideration    of  the 
forms  of  river  valleys  as  shown  in  cross-section. 

The  typical  river  valley  is  bounded  by  two  hill 
slopes,  each  possessing  the  denudation  curve,  and  if 
conditions  are  uniform,  the  cross  -  section  of  the 
valley  will  show  an  outline  similar  to  that  repre- 
sented in  Fig.  25  a,  while  if  we  take  a  longitudinal 
section  from  the  watershed  to  the  mouth  of  the 
river,  along  the  valley-bottom,  the  denudation  curve 
will  appear  as  seen  in  Fig.  25  b,  though  here  the 
lower  part  of  the  curve  will  probably  approximate  to 
a  straight  line  for  a  considerable  part  of  its  course.1 

1  An  English  term  for  the  line  taken  by  the  course  of  a  river  apart 
from  its  meanderings  is  much  needed,  and  we  are  driven  to  use  the 
German  term  Thaliueg  for  this  line. 


VALLEYS  127 

In  the  case  of  a  consequent  valley  formed  under 
uniform  conditions,  the  curve  will  be  bilaterally  sym- 
metrical, whereas  in  a  subsequent  valley  the  curve 
will  be  greater  on  the  escarpment  side  than  on  the 
side  of  the  dip-slope  as  seen  in  Fig.  23. 

Writers  sometimes  speak  of  river  valleys  as 
I-shaped,  V-shaped,  U-shaped,  and  Y-shaped,  accord- 
ing to  the  slopes,  which  roughly  recall  those  of  the 
letters  with  which  they  are  compared,  but  all  valleys 
of  erosion  will  be  ideally  U-shaped,  though  the  arms 
of  the  U  will  depart  from  verticality  and  become 


FIG.  25. 

a  =  Cross-section  of  a  valley  of  erosion. 
£  =  Line  of  Thalweg. 

separated  to  a  greater  or  less  extent,  according  to 
certain  conditions  controlling  erosion,  the  principal  of 
which  are  the  nature  of  the  rock,  the  character  of  the 
weathering,  and  the  occurrence  of  earth  movement,  and 
of  these  the  nature  of  the  rock  is  really  of  import- 
ance mainly  because  the  weathering  is  influenced  by 
it,  as  soft  rocks  weather  more  readily  than  hard  rocks. 
If  a  rock  resists  weathering,  the  rivers  will  cut 
narrower  valleys  than  when  the  rock  is  readily 
weathered.  This  is  seen  by  the  fact  that  narrow 
gorges  are  apt  to  occur  in  rainless -regions,  though 
there  are  many  exceptions  to  this,  and  under  suitable 
circumstances  extremely  narrow  gorges  can  be  formed 
in  regions  of  considerable  rainfall.  It  is  also  well 
shown  by  the  formation  of  those  peculiar  structures 


128     SCIENTIFIC   STUDY   OF   SCENERY 

known  as  earth-pillars  in  districts  where  the  condi- 
tions are  suitable  for  their  formation,  and  as  these 
earth-pillars,  when  well  developed,  are  apt  to  excite 
the  curiosity  of  those  who  see  them,  we  may  devote 
a  short  space  to  their  description. 

When  a  river  runs  through  a  compact  homo- 
geneous clay  charged  with  large  stones,  as  shown 
in  Fig.  26,  it  cuts  out  a  gorge  with  the  characteristic 
denudation  curve  a  b  c.  If  the  rainfall  is  great,  and 
fairly  vertical,  the  stones  act  like  umbrellas,  and 
protect  the  clay  immediately  beneath,  while  the 


FIG.  26. 

intervening  clay  is  washed  away  by  the  rain  and 
carried  into  the  river.  Accordingly  the  stone- 
protected  masses  stand  up  as  pillars,  the  sides  of 
\vhich  are  furrowed  by  rain  trickles,  and  they  often 
possess  minor  pinnacles  and  buttresses,  due  to  other 
stones  occurring  in  the  mass  of  the  column.  Now, 
if  the  stones  had  not  been  in  the  clay,  the  whole 
of  the  clay  would  have  been  washed,  away  by  rain 
action,  and  instead  of  the  gorge  a  c  b  we  should 
meet  with  a  wider  valley,  d  b  f.  The  pillars  which 
occur  near  Botzen,  in  the  Tyrol,  are  fully  described  and 
figured  by  Sir  C.  Lyell  in  his  Principles  of  Geology 
(vol.  i.,  chap,  xv.,  and  Plate  II.);  they  vary  in 
height  from  twenty  to  a  hundred  feet.  The  pillars 
near  Stalden,  above  Visp,  are  well  known,  and 


VALLEYS  129 

some  admirable  examples  are  found  at  Useigne,  in 
the  Val  d'Herens,  where  the  process  of  formation 
is  well  shown.  They  are  carved  out  of  the  material 
of  the  terminal  moraine  of  the  ancient  Val  d'Here- 
mence  glacier.  This  moraine  has  been  carved  out 
into  sharp  ridges  by  stream  action,  and  the  ridges  are 
further  cut  up  by  rain  to  form  the  pyramids,  which 
are  cut  through  by  the  road  to  Evolena,  on  either 
side  of  the  mouth  of  the  Val  d'Heremence,  though 
the  pillars  of  the  upper  group  are  more  striking 
than  those  of  the  lower. 

One  of  the  most  important  conditions  for  the 
formation  of  a  steep  gorge  is  the  occurrence  of  a 
swift  stream  which  can  corrade  rapidly,  in  which 
case  weathering  action  cannot  widen  the  gorge  to 
any  extent  while  the  river  is  deepening  it.  The 
swiftness  of  the  stream  may  be  due  primarily  to  uplift, 
and  this  is  no  doubt  the  most  important  factor  in 
producing  steep-sided  streams.  When  the  upper  part 
of  a  river-course  is  being  elevated,  while  the  lower 
part  is  stationary,  corrasion  will  be  increased,  and 
a  gorge  will  be  formed.  To  this  cause,  as  well  as 
to  the  arid  climate,  the  extraordinary  canons  of 
the  Colorado  region  are  due.  It  follows  that  when 
a  river  has  reached  its  base-level  of  erosion,  and 
downward  corrasion  is  stopped,  the  action  of  the 
weather  will  be  very  pronounced,  and  accordingly 
a  gorge  is  not  likely  to  exist  for  long  periods  in 
a  rainy  region  when  the  base-level  of  erosion  has 
been  established.  There  are  many  secondary  causes 
which  increase  the  corrasive  power  of  a  river  over 
parts  of  its  course,  and  gorges  may  be  carved  out 
there ;  for  instance,  as  already  seen,  a  waterfall  will 
form  a  gorge,  and  we  shall  show  in  the  sequel  that 


130    SCIENTIFIC   STUDY   OF   SCENERY 

many  waterfalls  are   due   to   secondary  changes   in 
river-courses. 

When  vertical  corrasion  and  weathering  are  both 
at  work,  the  width  of  the  valley  will  depend  on 
their  relative  importance ;  but  when  the  base-level 
of  erosion  is  reached,  important  changes  in  the 
action  of  the  river  occur,  which  must  now  be 
considered. 

So  long  as  vertical  corrasion  is  in  operation, 
lateral  corrasion  of  the  side  of  the  river-bed  is  in- 
significant ;  but  as  soon  as  vertical  corrasion  is 
checked  by  the  establishment  of  the  base-level  of 
erosion  lateral  corrasion  becomes  important,  and 
the  rivers  work  sideways  instead  of  downward, 
though  the  width  of  the  river  is  not  necessarily 
increased  thereby,  for  compensation  is  made  for 
corrasion  of  one  bank  by  deposition  on  the  opposite 
one.  We  have  already  noted  that  the  courses  of 
streams  are  unlikely  to  be  actually  straight  in  nature, 
as  the  river,  on  its  initiation,  will  be  turned  from 
side  to  side  by  minor  inequalities.  Imagine  a  portion 
of  a  river-course  flowing  in  the  direction  indicated 
in  Fig.  27,  that  is  from  x  toy,  and  that  it  has  a  slight 
S  -  shaped  curve  owing  to  some  inequality  in  its 
course.  In  the  straight  part  of  a  river-course  the 
centre  of  the  stream  flows  more  rapidly  than  the 
sides,  and  the  top  than  the  bottom,  as  the  stream 
is  retarded  by  friction  against  the  bottom  and  sides. 
Now  when  the  stream,  after  traversing  a  straight 
portion  of  its  course,  reaches  the  curve  represented 
in  the  figure,  the  central  swift  part  tends  to  flow 
on  in  the  same  straight  line,  and  impinges  against 
the  concave  bank  at  x,  eroding  it,  while  an  eddy 
is  set  up,  which  causes  the  current  to  flow  backward 


VALLEYS  131 

on  the  convex  side,  x',  and  to  deposit  material 
there.  The  same  process  takes  place  at  y,  and,  as 
a  result,  the  S-shaped  curve  becomes  emphasised, 
as  shown  by  the  -dotted  lines,  and  the  river  has  a 
cross  -  section  like  that  of  b,  Fig.  27,  which  is  a 
section  taken  from  y'  to  y  in  a.  The  whole  of  the 
S  -  shaped  curve  tends  to  work  down  the  valley 


FIG.  27. 

owing  to  the  general  slope  of  the  Thalweg ;  and 
accordingly,  when  a  river  has  reached  its  base-line 
of  erosion,  it  tends  to  widen  its  valley,  and  to  form 
a  plane  surface  which  slopes  gently  towards  the 
ocean.  Through  this  plain  the  river  meanders  in 
loop-shaped  folds.  During  flood  -  times  the  river 
overflows  its  banks,  and  in  the  slack  water  of  the 
flooded  portions  sediment  is  deposited  in  the  form 
of  alluvium,  which  may  build  up  the  floor  of  the 


132     SCIENTIFIC   STUDY   OF   SCENERY 

valley  to  a  considerable  height  above  the  level 
which  it  reached  when  the  base-line  of  erosion  was 
established.  These  alluvial  flats  mark  various  parts 
of  river  -  courses,  though  they  are  usually  more 
numerous  in  the  lower  portions.  A  cross  -  section 
of  a  valley  under  these  conditions  will  be  as 
follows  :  — 


Alluvial  Flat; 


FIG.  28. 


When  the  S-shaped  folds  have  been  growing  for 
some  time,  they  may  form  almost  complete  circles, 
and  during  floods  the  river  may  cut  through  the 
isthmus  which  separates  portions  of  two  loops,  when 
the  old  course  will  be  left  as  a  crescentic  lake. 

"A  multitude  of  such  crescent-shaped  lakes,  scattered 
far  and  wide  over  the  alluvial  plain,  the  greater  number 
of  them  to  the  west,  but  some  of  them  also  eastward  of 
the  Mississippi,  bear  testimony  to  the  extensive  wanderings 
of  the  great  stream  in  former  ages." x 

After  the  establishment  of  an  alluvial  flat  by 
lateral  corrasion  accompanied  by  deposition  the 
plain  will  remain  unaltered  in  its  general  characters, 
though  it  may  increase  in  width,  so  long  as  conditions 
remain  the  same.  Should  the  power  of  the  stream 
to  exert  vertical  corrasion  be  restored  to  it  in  any 
way,  it  will  again  cut  downward,  and  a  valley  within 
a  valley  will  be  formed,  as  shown  in  Fig.  29,  in  which 
a  exhibits  a  symmetrical  cross -section,  where  the 
river-course  happened  to  be  in  the  centre  of  the 
alluvial  plain  at  the  time  that  vertical  corrasive 
1  LYELL,  Sir  C.,  Principles  of  Geology ',  vol.  i.,  chap.  xix. 


VALLEYS  133 

power  was  restored,  while  b  shows  an  unsymmetrical 
cross -section,  with  the  later  part  of  the  valley  to- 
wards one  side  of  the  earlier  portion.  This  diagram 
illustrates  the  character  of  the  Grand  Canon  of  the 
Colorado,  which  is  a  valley  within  a  valley.  It  is 
clear  that  the  loops  which  were  formed  when  the 
base-level  of  erosion  had  been  temporarily  attained 
will  still  be  retained,  and  as  a  consequence  of  the 
pause,  followed  by  downward  erosion,  we  are  fur- 
nished with  those  remarkable  cases  of  narrow  valleys 
which  run  with  very  winding  courses,  such  as  the  two 


Crooks  of  Lune,  above  Lancaster  and  Kirkby  Lons- 
dale,  and  the  great  bend  of  the  Wear  around  Durham 
Cathedral. 

Restoration  of  the  power  of  a  stream  to  corrade 
vertically  may  be  due  to  several  causes,  the  chief  of 
which  is  uplift  of  the  land  along  the  upper  course 
of  the  stream,  which,  as  already  pointed  out,  in- 
creases the  velocity  of  the  stream.  Besides  this 
there  are  minor  causes,  which  are  of  importance, 
which  may  be  briefly  noticed,  and  some  of  their 
effects  considered.  Increase  in  the  amount  of  rain- 
fall, or  diminution  of  the  supply  of  sediment  to  a 
fully  charged  stream,  or  diversion  of  one  stream  into 
another  (in  ways  to  be  presently  described),  thereby 
increasing  the  volume  of  the  second  stream,  may 
restore  the  stream's  power  to  corrade  vertically.  The 
most  interesting  of  the  minor  causes,  however,  is 


134     SCIENTIFIC   STUDY   OF   SCENERY 

the  existence  of  hard  and  soft  rocks  which  alternate 
with  one  another  along  the  course  of  a  stream. 
Suppose  that  a  consequent  stream  is  flowing  across 
alternate  stratified  deposits  of  hard  sandstone  and 
soft  shale,  as  in  Fig.  30.  The  shale  is  more  readily 
denuded  than  the  sandstone  under  ordinary  circum- 
stances, but  a  bed  of  shale  cannot  be  corraded  to 
an  appreciably  greater  depth  than  the  sandstone  sur- 
face which  occurs  lower  down  the  stream,  or  a  pond 
would  be  formed  filled  with  still  water,  which  could 


B 

FIG.  30. 

not  corrade.  Accordingly  if,  as  in  the  figure,  a  con- 
sequent stream  flows  along  the  course  A  B  in  the 
direction  of  the  arrow,  the  soft  shale  5  between 
the  two  hard  beds  H  H'  may  be  worn  down  to  a 
nearly  level  surface,  as  represented  by  the  dotted 
line  i  2,  but  it  cannot  be  worn  lower.  The  stream 
here  will  have  formed  a  temporary  base-line  of 
erosion,  and  the  same  process  will  go  on  in  the 
shale  S'.  As  the  hard  beds  H'  H"  are  not  worn 
away  so  rapidly,  the  result  of  lowering  the  level 
of  the  upper  surface  of  the  shale  vS  will  be  that  the 
slope  of  the  stream  is  increased  where  the  river 
passes  from  H'  to  S  at  2,  and  a  gorge  will  be 
formed,  and  the  river  will  gradually  lower  its  bed 
along  H',  as  shown  by  the  dotted  line  2  3  ;  and 


VALLEYS  135 

then  the  portion  of  the  stream  running  through  the 
soft  shale  S'  can  be  lowered,  and  formation  of  a 
gorge  will  commence  in  H",  the  course  of  the  stream 
being  finally  along  the  dotted  line  1234.  It  will 
be  seen  that  the  portion  of  the  stream  flowing  over 
S',  which  had  temporarily  established  its  base-line 
of  erosion,  5  6,  before  the  hard  rock  H'  was  corraded, 
is  again  capable  of  exerting  a  corrasive  influence 
under  the  changed  conditions,  and  the  cross-section 
of  that  part  of  the  valley  situated  over  S'  will  appear 
as  in  Fig.  29. 

It  follows  from  the  above  that  a  valley  initiated  in 
a  country  composed  of  alternating  soft  and  hard  rocks 
will  be  occupied  by  a  river  alternately  flowing  over 
gentle  slopes  and  more  abrupt  ones,  and  that 
corrasion  of  the  abrupt  slopes  will  cause  the  river 
to  cut  back  into  the  gentle  ones,  producing  the 
Y-shaped  cross -section,  which  may  be  repeated 
more  than  once.  In  the  end  hard  and  soft  rocks 
will  be  cut  down  till  the  base-line  of  corrasion  is 
reached,  and  accordingly  alternation  of  rapids  and 
cascades  in  a  gorge  with  a  sluggish  stream  along 
a  flat  can  only  occur  in  a  young  river  or  in  an  old 
one  which  has  been  affected  by  disturbing  influences, 
for  a  rapid  river  which  is  charged  with  detritus  and 
has  been  in  existence  for  a  long  period  will  cut  its 
channel  till  it  has  attained  its  base-level;  for  instance, 
the  Colorado  in  a  course  of  1000  miles  falls  over 
5000  feet,  and  yet  no  waterfall  is  met  with  through 
the  whole  of  this  portion  of  its  course.  To  the 
subject  of  waterfalls  we  shall  recur  in  the  next 
chapter.  It  need  only  be  stated  that  the  valley  is 
likely  to  be  narrow  in  the  hard  rocks  and  wider 
where  it  traverses  the  softer  ones. 


136     SCIENTIFIC   STUDY   OF   SCENERY 

When  a  river  temporarily  attains  its  base-line  of 
erosion,  and  subsequently  becomes  capable  of  cor- 
rading  its  bed  vertically,  if  the  main  stream  has  a 
longer  course  than  its  tributaries  it  will  probably 
possess  a  greater  volume  of  water  than  that  of  each 
tributary,  and  may  corrade  to  a  considerable  depth, 
while  the  tributaries  exert  little  influence,  notwith- 
standing the  increase  of  slope.  For  a  considerable 
period  after  the  deepening  of  the  main  valley,  the 
minor  valleys  will  end  as  definite  gorges  some  height 
above  the  floor  of  the  main  valley,  and  discharge 
their  waters  in  a  series  of  cascades  or  falls  down  the 
side  of  the  main  valley,  and  this  period  may  be 
lengthened  owing  to  minor  causes.  In  a  district 
like  the  Lake  District  many  of  the  major  valleys, 
like  that  in  which  Thirlmere  is  situated,  rise  from 
comparatively  low  cols,  and  the  main  stream  is  not 
supplied  with  a  very  large  supply  of  sediment  near 
its  source.  The  tributary  valleys  rising  amongst  the 
frost-shattered  ridges  of  the  higher  hills  are  supplied 
with  a  quantity  of  material  for  transportation,  and 
their  power  of  corrasion  of  the  unweathered  rocks  in 
the  lower  part  of  their  course  is  greatly  diminished, 
as  their  energy  is  mainly  available  for  transportation 
only. 

Accordingly  we  find  in  the  Lake  District  a 
number  of  tributary  valleys  occurring  in  the  hearts 
of  the  ridges,  and  opening  out  far  above  the  bottoms 
of  the  main  valleys,  discharging  their  waters  down 
the  slopes  in  cascades.  They  are  specially  well 
marked  on  the  east  side  of  Helvellyn,  and  a  number 
of  them  also  open  into  the  upper  branches  of  Borrow- 
dale. 


VALLEYS  137 

Now,  let  the  river  of  the  main  valley  once  more 
attain  its  base-level  of  erosion,  and  form  an  alluvial 
plain.  The  material  which  is  brought  down  the  hill- 
sides by  streamlets  is  deposited  in  the  form  of  "  dry 
deltas"  when  the  velocity  of  the  streamlets  is  checked 
on  reaching  the  plain,  and  the  major  streams  which 
issue  from  the  upland  valleys  just  described  build 
deltas  of  considerable  size,  assuming  the  shape  of 
half  a  cone,  with  its  apex  coinciding  with  the  point 
at  which  the  tributary  stream  issues  from  the  hill- 
side to  tumble  down  the  slope  of  the  main  valley, 
and  accordingly  a  series  of  more  or  less  symmetrical 
"  alluvial  cones "  are  formed  around  the  mouths  01 
these  valleys. 

The  dry  delta  is,  of  course,  formed  whenever  a 
rapidly  running  tributary  charged  with  much  material 
enters  into  a  main  river  flowing  over  a  surface  so 
gently  inclined  that  it  cannot  transport  the  sediment 
brought  down  by  the  tributary.  Now  the  water  of  the 
tributary  is  impelled  against  the  opposite  side  of  the 
main  river,  producing  corrasion  of  the  bank  there, 
and  the  formation  of  the  dry  delta  drives  the  main 
stream  to  the  opposite  side  of  the  valley,  and,  as  a 
consequence,  main  streams  tend  to  bend  away  from 
their  tributaries  where  these  join  them.  Admirable 
examples  are  found  in  the  upper  course  of  the  Rhone 
valley,  where  it  wanders  through  the  flat  marshes 
between  Brieg  and  Martigny,  the  best  being  just  east 
of  Sion.  Here  the  rapid  Borgne,  draining  the  Val 
d'Herens  and  Val  d'Heremence  to  the  south,  drives 
the  Rhone  against  its  northern  bank,  while  a  little 
further  east  the  Riere,  flowing  from  the  Wildstrubel 
group  to  the  north,  forces  the  Rhone  to  its  southern 
bank  near  St.  Leonhard. 


138     SCIENTIFIC   STUDY   OF   SCENERY 

If  a  great  quantity  of  debris  is  carried  into  a  main 
valley  in  this  way,  it  may  ultimately  result  in  the 
formation  of  a  lake,  occupying  the  portion  of  the 
valley  above  the  junction  of  the  tributary,  a  process 
which  will  be  more  fully  described  in  a  future 
chapter. 


CHAPTER  X. 

VALLEYS   (Continued] 

WE  have  hitherto  assumed  that  river  systems 
are  initiated  as  the  result  of  uplift  of  an  area 
composed  of  stratified  rocks  which  were  originally 
horizontal.  These  river  systems  are  described  by 
Gilbert  as  consequent  upon  the  uplift  (the  term  con- 
sequent being  here  used  in  a  wider  sense  than  that 
in  which  it  is  applied  by  Davis),  and  we  have 
considered  the  conditions  of  drainage  which  would 
exist  in  the  case  of  a  symmetrical  uplift,  which 
must  be  in  accordance  with  the  laws  which  control 
them. 

We  must  now  refer  to  the  complications  which 
will  result  owing  to  departure  from  uniformity. 

In  the  first  place,  actual  drainage  lines  may  differ 
from  those  which  would  be  developed  under  ideal 
uniform  conditions,  on  account  of  differences  in  the 
hardness  of  rocks ;  any  rock  or  any  fracture  or 
system  of  fractures  which  permits  weathering  and 
corrasion  to  occur  more  readily  than  among  the 
neighbouring  rocks  tends,  if  other  conditions  permit, 
to  give  rise  to  valleys.  Accordingly  the  ideal  alter- 
nate tributaries  entering  a  main  stream  are  often 
partly  replaced  by  two  tributaries  entering  the  stream 
at  the  same  point,  the  production  of  these  being 
determined  by  a  plane  of  weakness,  and — a  matter  of 
139 


140     SCIENTIFIC   STUDY   OF   SCENERY 

greater  importance  from  our  present  standpoint — 
tributaries  of  adjoining  rivers  may  start  from  the 
same  position  on  the  watershed,  giving  rise  to  a 
depression  at  the  top,  which  is  not  placed  laterally 
to  the  valley  heads,  but  occurs  at  the  heads,  and 
accordingly  a  valley  of  this  character  is  not  domi- 
nated by  a  mountain  peak,  and  the  valley  loses  one 
of  its  principal  scenic  attributes.  The  valley  of 
Thirlmere  and  the  corresponding  valley,  in  which 
Grasmere  is  situated,  are  separated  by  the  pass  of 
Dunmail  Raise,  which  is  of  this  character.  The  effect 
of  planes  of  weakness  in  giving  rise  to  pyramidal 
hills  by  severance  of  the  lateral  ridge  has  already 
been  considered. 

Another  complication  may  be  produced  when  a 
river  has  established  its  base-level  of  erosion.  It 
has  been  seen  that  lateral  corrasion  becomes  im- 
portant ;  a  river  then  eats  into  its  banks,  and  it  may 
eventually  cut  through  the  ridge  separating  it  from 
an  adjoining  river,  when  the  upper  waters  of  the 
river  at  a  higher  level  are  switched  off,  and  become 
tributaries  to  the  river  at  a  lower  level,  while  the 
lower  waters  start  from  a  freshly  formed  col.  Many 
minor  complications  may  result  from  this,  such  as 
increased  erosive  power  of  the  one  river,  owing  to 
increase  of  volume,  causing  deepening  of  its  valley, 
and  diminished  erosive  power  of  the  other  stream. 
The  new  col  will  not  be  dominated  by  a  mountain 
peak,  unless  that  at  the  head  of  the  original  valley  is 
visible  from  the  shortened  valley.  . 

Other  complications  are  produced  according  to 
what  Gilbert  terms  the  law  of  unequal  slopes.  In 
Fig.  31,  suppose  the  line  C  A  C'  to  represent  a 
section  across  an  unsymmetrical  uplift  with  a  steep 


VALLEYS  141 

slope  A  C,  and  a  gentle  one  AC'.  Weathering  and 
corrasion  will  occur  more  extensively  along  A  C 
than  along  AC',  and  so,  while  a  small  thickness  of 
rock,  C'  .D',  is  worn  away  on  the  side  of  the  gentle 
slope,  a  much  greater  thickness,  C  D,  will  be 
denuded  on  the  steeper  slope,  and  the  result  is  that 
the  watershed  is  shifted  laterally  from  A  to  B,  and 
any  tributaries  of  the  streams  coursing  down  the 


FIG.  31. 

gentle  slope  and  entering  them  between  A  and  B 
will  be  diverted  into  the  streams  flowing  down  the 
steep  slope.  The  recession  of  the  watershed  will  be 
continuous  all  along  owing  to  weathering,  but  will  be 
most  marked  at  the  heads  of  the  major  streams,  and 
accordingly  we  may  have  gorges  cut  into  the  side^4  C, 
extending  backwards  and  forming  deep  gashes  in 
the  gentler  valleys  on  the  side  A  C',  as  is  well  seen 
in  the  valley  of  High  Cup  Gill,  near  Appleby,  in 
Westmorland,  which  has  cut  far  backward  into  a 
shallow  tributary  of  the  Tees.1  Here  we  have 

See  Geographical  Journal,  vol.  vii.,  p.  607. 


142     SCIENTIFIC   STUDY   OF   SCENERY 

another  case  of  a  valley  which  will  not  be  dominated 
by  a  peak  at  the  head. 

The  law  of  unequal  slopes  may  control  erosion 
when  adjoining  valleys  are  at  different  levels  if  the 
lower  valley  receives  the  waters  of  subsequent 
valleys.  The  subsequent  valley  falling  into  the 
lower  stream  will  have  greater  erosive  power  than 
its  neighbour  over  the  col,  and  may  gradually  extend 
its  course  backward  till  it  beheads  the  adjoining 
consequent  stream,  which  will  thus  have  its  head 
waters  diverted  to  the  consequent  stream  existing 
at  a  lower  level.  In  this  way  Professor  Davis,  in  the 
paper  cited  in  the  last  chapter,  accounts  for  many 
complications  in  the  drainage  of  East  Anglia,  and  it 
is  this  process  which  appears  to  have  severed  the 
ridge  extending  northward  from  the  Matterhorn,  for 
at  one  time  the  stream  in  the  Zinal  valley  seems  to 
have  had  its  source  about  the  Tete  de  Valpelline,  and 
ran  northward  over  the  Zinal  Joch,  and  was  subse- 
quently beheaded  by  the  river  occupying  the  valley 
of  the  present  Zmutt  glacier,  which  severed  the  ridge 
between  the  upper  part  of  the  original  Zinal  valley 
and  the  Nikolai-thai.  Obsequent  streams  flowing 
down  the  steep  faces  of  escarpments  cut  back  their 
heads,  often  forming  combes,  but  as  the  adjoining 
subsequent  stream  at  the  foot  of  the  dip  -  slope  is 
naturally  at  a  lower  level  than  that  beneath  the 
escarpment,  actual  beheading  will  only  occur  under 
exceptional  conditions. 

Change  of  drainage  lines  may  occur  owing  to  the 
existence  of  alluvial  cones,  though  the  results  are 
insignificant  to  the  student  of  scenery.  If  a  cone  be 
formed  at  the  col  separating  two  important  valleys 
by  a  tributary  entering  the  main  valley  close  to  the 


VALLEYS  143 

watershed,  as  the  water  shifts  its  position  on  the  cone, 
deserting  the  channels  which  it  has  built  up  to  some 
height  above  the  general  level,  the  water  will  flow  now 
to  one  main  stream,  at  another  time  to  the  other. 
A  good  case  is  exhibited  on  Dunmail  Raise,  where 
a-  tributary  coming  down  the  Helvellyn  range  has 
formed  an  alluvial  cone  on  the  watershed.  The 
tributary  drains  towards  Grasmere  at  present,  but  a 
small  dry  valley  below  the  base  of  the  cone  towards 
Thirlmere  shows  that  it  flowed  in  that  direction  at  no 
distant  date. 

The  last  mode  of  diversion  of  drainage  lines  to 
which  we  shall  call  attention  is  described  by  Gilbert 
under  the  name  of  ponding.  Either  by  subsequent 
uplift  or  by  formation  of  a  dam,  a  lake  is  formed 
along  a  river -course.  We  shall  discuss  the  forma- 
tion of  lakes  in  detail  in  a  separate  chapter.  If 
the  dam  is  lower  than  all  the  cols  higher  up  the 
valley,  the  water  issues  from  the  lake  over  its  original 
position,  and  no  diversion  of  drainage  occurs ;  but  if 
a  col  exists  higher  up  the  valley  with  its  notch  at 
a  lower  level  than  that  of  the  lowest  part  of  the 
barrier,  the  water  of  the  lake  escapes  over  this  col, 
and  a  permanent  diversion  of  drainage  takes  place, 
the  ponded  valley  being  beheaded  by  the  uplifted  or 
accumulated  barrier. 

The  main  scenic  effects  due  to  diversions  of  drain- 
age, causing  beheading  of  one  valley  and  addition  to 
the  waters  of  an  adjoining  one,  are  (i)  production 
of  pyramidal  mountains  by  severance  of  a  ridge, 
culminating  in  a  peak ;  (ii)  formation  of  cols  or 
passes  which  are  on  the  medial  line  of  a  valley, 
and  accordingly  the  valley  head  is  not  dominated 
by  a  peak;  (iii)  production  of  dry  valleys,  often  of 


144     SCIENTIFIC   STUDY   OF   SCENERY 

considerable  extent,  beneath  the  new  col,  produced 
by  diversion  of  the  head  waters  of  the  valley  into  an 
adjoining  valley :  as  these  valleys,  owing  to  absence 
of  any  large  volume  of  running  water,  allow 
weathered  material  to  accumulate,  upon  which  a 
marsh  vegetation  often  flourishes,  they  are  apt  to 
present  a  particularly  desolate  aspect ;  (iv)  pro- 
duction of  waterfalls,  as  described  in  the  latter  part 
of  the  chapter. 

Drainage  has  been  hitherto  considered  as  though 
it  were  always  due  to  emergence  of  strata  from 
the  sea,  but  we  may  have  an  uplift  of  a  tract 
of  land  which  has  been  reduced  to  a  nearly  level 
surface,  or  peneplain,  by  subaerial  denudation,  when 
the  watershed  will  coincide  with  the  axis  of  uplift, 
but  will  have  no  necessary  relation  to  the  inclination 
of  the  partly  denuded  strata,  for  they  owe  this  in- 
clination to  a  previous  movement.  We  may  now 
proceed  to  consider  what  Gilbert  terms  inconsequent 
drainage,  which  he  divides  into  two  classes,  namely, 
antecedent  drainage  and  superinduced  drainage. 

When  an  uplift  takes  place  across  a  river-course, 
we  have  seen  that  the  stream  may  be  ponded  back. 
If,  however,  the  uplift  is  very  slow,  and  the  corrasive 
action  of  the  stream  rapid,  the  stream  may  keep  its 
course  open,  notwithstanding  the  uplift,  just  as  in 
a  fixed  saw,  when  a  log  is  pressed  up  against  it,  the 
saw  works  in  the  same  line,  and  cuts  a  fissure  through 
the  log.  As  the  result  of  this  process,  rivers  may 
run  through  mountains,  and  a  gorge  be  formed. 
A  similar  result  may  follow  owing  to  superim- 
posed drainage,  and  it  is  in  many  cases  difficult 
to  distinguish  one  process  from  the  other.  The 
course  of  the  Green  river  through  the  Uinta  moun- 


VALLEYS  145 

tains  has  been  ascribed  by  Powell  as  due  to  ante- 
cedent drainage,  i.e.,  drainage  antecedent  to  the 
uplift,  and  Medlicott  and  Blanford  thus  explain  the 
course  of  the  Indus  and  the  Brahmaputra  through 
the  Himalayas.1 

Superimposed  drainage  may  occur  as  the  result  of 
formation  of  plains  by  lateral  corrasion,  this  is  the 
drainage  superimposed  by  planation,  to  use  Gilbert's 
expression  ;  or  the  drainage  may  be  imposed  upon 
deposits,  whether  terrestrial,  as  alluvium,  or  marine, 
as  ordinary  sediments.  Drainage  in  this  case  is 


superimposed  by  alluviation  or  sedimentation.  Upon 
uplift  the  drainage  will  coincide  with  the  axis  of 
uplift,  but  when  the  superficial  deposits  have  been 
worn  away,  the  drainage  will  have  no  apparent 
relation  with  the  inclination  of  the  unconformable 
strata  beneath  the  overlying  eroded  deposits ;  thus 
the  axis  of  the  anticlinal  fold  of  a  ridge  need  not 
underlie  the  main  watershed.  This  is  illustrated  in 
Fig.  32,  which  is  a  section  across  the  English  Lake 
District.  (See  also  Chapter  VI.) 

The  older  strata  xx  were  formerly  bent  into  an  arch 
with  its  axis  about  the  head  of  the  arrow  A.  These 
arched  strata  were  denuded  to*  an  approximately 

1  It  is  only  right  to  state  that  some  cases  of  asserted  antecedent 
drainage  have  been  disputed  by  Professor  W.   M.  Davis,  but  this  is 
not  the  place  to  discuss  controversial  questions. 
L 


146     SCIENTIFIC   STUDY   OF   SCENERY 

level  surface  before  the  deposition  of  the  strata  y  y 
upon  them.  The  latter  were  originally  deposited 
horizontally,  and  subsequently  uplifted  around  a 
point  situated  about  the  position  of  the  head  of 
the  arrow  B,  and  a  radial  drainage  was  initiated, 
which  was  consequent  to  the  second  uplift,  and,  as 
far  as  the  rocks  y  y  are  concerned,  was  an  ordinary 
case  of  consequent  drainage.  The  strata  y  y  have 
since  been  denuded  over  the  centre  of  the  district 
(their  former  extension  being  indicated  by  the  dotted 
lines),  and  the  drainage  is  superimposed  upon  the 
older  strata  x  x  and  is  inconsequent  so  far  as  their 
axis  of  uplift  at  A  is  concerned. 

The  original  consequent  and  subsequent  streams 
will  run  approximately  in  their  original  directions 
after  they  have  reached  the  older  rocks,  but  a  number 
of  minor  streams  will  be  developed,  owing  to  the 
occurrence  of  planes  of  weakness  among  the  older 
rocks  which  did  not  extend  into  the  newer  ones. 
Thus  in  the  Lake  District  the  consequent  streams, 
as  those  occupying  the  Keswick,  Coniston,  Winder- 
mere,  and  Ullswater  valleys,  run  in  the  direction 
which  was  determined  by  the  uplift  of  the  strata 
which  have  now  been  eroded,  though  they  have  under- 
gone minor  modifications  as  the  result  of  the  different 
nature  of  the  rocks  over  which  the  streams  now 
course,  but  tributary  valleys  have  been  developed, 
which  owe  nothing  to  the  once  overlying  strata. 
Such  a  valley  is  the  Vale  of  Troutbeck,  determined 
by  the  occurrence  of  a  great  belt  of  broken  rock, 
and  accordingly  marked  by  very  steep,  parallel  sides, 
and  a  similar  origin  may  be  ascribed  to  the  two 
valleys  which  start  from  Dunmail  Raise. 

When  an  area  has  been  reduced  to  a  plain  sur- 


VALLEYS  147 

face  by  subaerial  denudation,  and  widespread  uplift 
occurs,  the  cycle  of  denudation  begins  afresh,  as 
described  by  Davis,  and  the  peneplain  will  be  cut 
up  by  denudation,  which  may  give  rise  to  new  hills, 
carved  out  of  the  plain,  and  marked  at  first  by  the 
possession  of  flat  tops ;  to  these  Davis  gives  the 
name  "  monadnocks,"  from  a  hill  in  New  Hampshire. 
An  example  is  figured  by  Gilbert  in  his  Geology  of  the 
Henry  Mountains  (Fig.  6). 

Before  leaving  the  consideration  of  the  causes 
which  may  give  rise  to  complications  of  drainage, 
one  suggested  cause  may  be  referred  to,  namely,  the 
rotation  of  the  earth  on  its  axis.  Of  this  Gilbert 
speaks  as  follows  : — 

"The  rotation  of  the  earth,  just  as  it  gives  direction  to 
the  trade  winds  and  to  ocean  currents,  tends  to  deflect 
rivers.  In  the  southern  hemisphere  streams  are  crowded 
against  their  left  banks,  and  in  northern  against  the  right. 
But  this  influence  is  exceedingly  small.  Mr.  Ferrel's  in- 
vestigations show  that  in  latitude  45°,  and  for  a  current 
velocity  of  ten  miles  an  hour,  it  is  measured  by  less  than 
one  twenty-thousandth  part  of  the  weight  of  the  water. 
(American  Journal  of  Science,  January,  1861).  If  its 
effects  are  ever  appreciable,  it  must  be  where  lateral 
corrasion  is  rapid,  and  even  there  it  is  probable  that  the 
chief  result  is  an  inclination  of  the  flood-plain  toward  one 
bank  or  the  other,  amounting  at  most  to  two  or  three 
minutes."1 

Waterfalls, — Reference  has  been  made  in  passing 
to  the  conditions  favourable  for  the  formation  of 
waterfalls,  but  on  account  of  their  prominent  in- 
fluence on  certain  types  of  scenery  they  deserve 
more  than  passing  mention. 

1  Geology  of  the  Henry  Mountains,  p.  136. 


148     SCIENTIFIC   STUDY   OF   SCENERY 

As  the  ultimate  effect  of  river  denudation  is  the 
production  of  the  base-line  of  erosion,  it  is  clear  that 
waterfalls  can  only  exist  in  the  courses  of  streams 
which  have  not  reached  the  base-level,  or  which, 
having  once  reached  it,  have  been  subjected  to  some 
change  which  has  restored  the  corrasive  power  of 
the  streams  over  parts  of  their  courses. 

In  the  early  history  of  a  consequent  stream  a 
waterfall  may  be  developed  at  any  point  where 
soft  rocks  are  formed  lower  down  the  stream  than 
hard  rocks,  so  that  the  soft  rocks  may  be  readily 
denuded,  and  the  hard  rocks  remain  undenuded  in 
the  bed  of  the  stream  for  a  considerable  time.  Thus, 
if  a  dyke  of  igneous  rock  traversing  soft  shales  be 
crossed  by  a  stream,  the  shales  below  the  dyke  may 
be  worn  away,  and  a  waterfall  produced  down  the 
vertical  wall  of  the  dyke.  Any  mass  of  hard  rock 
in  contact  with  soft  rock  may  thus  cause  a  fall.  A 
good  example  is  furnished  by  Scale  Force,  near 
Buttermere,  in  the  Lake  District,  which  is  due  to 
the  erosion  of  soft  clay  rock  and  the  resistance  of 
a  mass  of  granitic  rock,  down  which  the  water  now 
falls.  Many  of  the  most  impressive  falls,  however, 
are  produced  in  gently  inclined  strata,  and  their 
formation  merits  fuller  description. 

Suppose  a  hard,  well-jointed  sandstone  or  lime- 
stone, a,  rests  upon  the  surface  of  a  deposit  of  soft 
shale,  b,  as  in  Fig.  33.  It  has  been  previously  shown 
that  where  the  shale  crops  out  in  the  bed  of  a 
stream  of  uniform  slope  the  shale  will  be  worn 
away  to  a  greater  extent  than  the  hard  rock,  and 
the  corrasive  power  of  the  stream  will  be  increased 
at  the  junction,  and  a  cascade  or  rapid  produced. 
After  the  establishment  of  the  cascade  the  action 


VALLEYS 


149 


of  the  water  becomes  somewhat  different.  The 
water  bringing  sediment  over  the  cascade  begins 
to  undermine  the  soft  deposit,  and,  as  in  the  case  of 
escarpments,  the  harder  rock  overhangs,  until  a  mass 
breaks  away  along  dominant  joint-planes,  and  the 
process  starts  afresh;  a  ravine  is  formed  in  this 
way,  and  the  waterfall  at  the  head  of  the  ravine 
gradually  recedes,  thus  lengthening  the  ravine. 
During  the  establishment  of  the  cascade  subsequent 
streams  may  form  valleys  along  the  strike  of  the 


FIG.  33. 


soft  shale,  giving  rise  to  an  escarpment,  and  it  is 
often  stated  that  a  waterfall  commenced  at  an 
escarpment,  but  with  a  young  consequent  river, 
waterfall  and  escarpment  may  be  formed  simul- 
taneously. 

Many  of  the  best-known  waterfalls  are  produced 
in  the  way  described  above.  In  England  the 
numerous  waterfalls  of  the  Yorkshire  dales,  as 
Thornton  Force,  near  Ingleton,  and  Hardraw  Force, 
in  Wensleydale,  are  due  to  the  existence  of  masses 
of  well-jointed  limestone  or  sandstone  upon  shale, 
and  High  Force,  in  Teesdale,  has  been  produced 
owing  to  the  occurrence  of  a  nearly  horizontal  sill  of 


150     SCIENTIFIC   STUDY   OF  SCENERY 

intrusive  rock  in  soft  sediments.  (See  plate.)  Niagara 
is  the  classic  example  of  a  waterfall  having  this 
structure,  and,  as  previously  stated,  a  full  description 
of  its  formation  will  be  found  in  Sir  Charles  Lyell's 
Principles  of  Geology,  while  the  geological  structure 
and  physical  features  of  the  country  surrounding  the 
gorge  and  fall  are  admirably  illustrated  in  the 
coloured  bird's-eye  view  of  the  falls  and  adjacent 
country  which  forms  the  frontispiece  to  the  first 
volume  of  the  same  author's  Travels  in  North 
America. 

Owing  to  the  sudden  change  of  volume  of  a 
stream  at  the  bottom  of  a  cirque,  cwm,  or  corrie, 
causing  sudden  increased  corrasion,  the  semicircular 
summit  of  the  amphitheatre  is  often  marked  by  a 
precipice,  and  any  streams  which  rise  on  compara- 
tively flat  ground  above  the  precipice  are  hurled 
down  its  side  as  waterfalls. 

It  has  already  been  stated  that  under  certain 
conditions  a  main  valley  may  undergo  further  cor- 
rasion, which  is  checked  in  the  case  of  tributary 
valleys,  opening  out  far  above  the  floor  of  the  main 
valley ;  the  tributary  streams  then  flow  down  the  side 
of  the  main  valley  as  cascades.  If  the  geological 
conditions  are  favourable,  these  cascades  may  be 
replaced  by  waterfalls.  An  example  is  seen  in  the 
case  of  the  well-known  Lodore,  in  Borrowdale,  where 
the  waters  of  the  deep  and  narrow  Watendlath  valley 
are  hurled  down  a  cliff  at  the  entrance  to  the  main 
valley. 

In  a  region  where  the  streams  have  established 
their  base-lines  of  erosion,  deviation  of  the  stream 
courses  in  any  of  the  various  methods  described  in 
the  earlier  part  of  the  present  chapter  may  give  rise 


VALLEYS  151 

to  waterfalls,  either  by  diversion  of  the  water  over 
existing  cliffs,  or  by  the  formation  of  falls  by  erosion 
of  the  softer  rocks  by  the  diverted  stream.  I  have 
recently  examined  a  large  number  of  the  minor 
waterfalls  of  Lakeland,  and  discovered  that  many 
of  them  owe  their  existence  to  recent  diversion  of 
stream-courses  by  the  formation  of  dams  of  glacial 
detritus  which  have  blocked  the  old  courses  of  the 
streams.  A  pretty  little  example  is  seen  in  the 
Langstrath  valley,  one  of  the  feeders  of  Borrowdale ; 
it  is  described  and  figured  in  the  Geographical 
Journal  (vol.  vii.,  p.  617,  and  figure  on  p.  618). 

The  course  of  the  stream  is  often  widened  and 
apparently  deepened  just  below  a  waterfall,  giving 
rise  to  a  deep,  often  more  or  less  circular,  pool,  which 
forms  one  of  the  characteristic  features  of  a  waterfall 
scene.  The  widening  is  due  to  the  production  of 
eddies,  which  cause  the  lateral  corrasion  of  the  cliffs 
below  the  fall.  The  deepening  is  due  to  the  force 
of  the  water  dashing  stones  and  sediment  against 
the  bottom  and  excavating  a  basin.  How  far  this 
process  can  occur  I  am  unable  to  state,  as  I  have 
found  no  detailed  description  of  the  formation  of  a 
large  rock-bound  pool  of  this  character,  though  that 
it  can  occur  to  some  extent  is  proved  by  the  forma- 
tion of  holes  of  some  size  below  a  waterfall.  I 
have  in  recent  years  examined  a  large  number  of 
pools  below  minor  waterfalls,  and  found  that  in 
many  cases  the  pool  is  essentially  due  to  accumu- 
lation of  loose  material  some  distance  below  the 
actual  fall.  The  force  of  the  stream  is  sufficient  to 
carry  away  the  transported  sediment  from  the  im- 
mediate foot  of  the  fall,  and  a  barrier  is  produced, 
damming  back  the  waters  to  form  a  pool.  This 


152     SCIENTIFIC   STUDY   OF  SCENERY 

barrier  is  raised  until  an  upward  slope  is  made  of 
sufficiently  low  gradient  to  allow  the  material  to  be 
carried  up  it  by  the  swiftly  flowing  stream.  If  the 
stream  flows  through  a  narrow  gorge  beneath  the 
fall,  the  force  of  the  stream  may  be  sufficient  to  carry 
the  material  through  the  gorge,  and  to  form  the  dam 
at  the  lower  end,  when  the  gorge  will  be  occupied  by 
water  of  some  depth.  To  this  is  due  the  very 
striking  appearance  of  the  gorge  below  the  little 
fall  in  the  Langstrath  valley  referred  to  above.  A 
barrier  has  been  formed  at  its  lower  end,  and  the 
gorge  itself  is  occupied  by  deep  water  of  extreme 
transparency,  and  of  a  lovely  green  hue,  due  to  the 
nature  of  the  rocks  at  its  side  and  stones  at  the 
bottom. 

Underground  Rivers. — In  districts  which  are  largely 
occupied  by  rocks  which  are  capable  of  being  carried 
away  in  solution  by  water  charged  with  solvents, 
an  underground  circulation  may  be  established, 
giving  rise  to  caves ;  and  as  the  interior  of  these 
caverns  is  often  of  great  interest  and  beauty,  it 
is  necessary  to  say  a  few  words  concerning  their 
formation  and  structure,  leaving  the  reader  who  is 
interested  in  the  subject  to  gather  further  information 
from  the  second  chapter  of  Professor  Boyd  Dawkins' 
work  on  Cave-hunting,  in  which  the  physical  history 
of  limestone  caverns  is  considered  at  some  length. 

A  porous,  soluble  rock  like  chalk  permits  drainage 
to  take  place  underground  to  a  considerable  extent, 
and  accordingly  we  meet  with  numerous  cases  of 
underground  streams  in  a  chalk  district;  hence  also 
the  general  absence  of  surface  drainage  over  the 
chalk,  except  when  large  streams  contain  a  volume 
of  water  so  great  that  only  a  portion  of  it  can  be 


VALLEYS  153 

absorbed.  The  chalk,  therefore,  is  often  marked 
by  dry  valleys,  the  origin  of  which  has  been  a 
subject  of  dispute,  though  the  suggestion  of  Mr. 
Clement  Reid  that  they  were  formed  at  a  time 
when  the  climate  was  sufficiently  rigorous  to  freeze 
the  water  in  the  surface-pores,  thus  stopping  the 
absorption  of  water  and  allowing  the  water  to 
establish  surface  streams,  satisfies  all  the  require- 
ments. 

It  is,  however,  in  the  case  of  hard  and  regularly 
jointed  limestone  rocks  that  we  meet  with  the  most 
striking  effects  of  underground  circulation,  exhibited 
in  our  own  country  in  the  limestone  rocks  of  York- 
shire, Derbyshire,  and  Somerset,  and  abroad  by  those 
of  Belgium,  Greece,  and  Kentucky. 

We  have  already  called  attention  to  the  formation 
of  plateaux  of  limestone,  with  gaping  fissures  worn 
along  the  master  -  joint  planes,  by  the  action  of 
acidulated  rain  water.  The  water  coursing  down 
the  ordinary  sediments,  sandstones,  and  clays,  which 
form  the  bed  of  the  stream  at  a  higher  level,  reaches 
one  of  these  fissures,  and  plunges  down  it.  A 
gyratory  motion  is  given  to  the  stones  and  sediment 
which  it  carries,  and  accordingly  the  stream  bores 
a  cylindrical  shaft  in  the  limestone,  locally  known 
as  a  "  pothole " ;  but  as  this  term  has  been  used  in 
a  different  sense,  the  term  "  swallow-hole "  is  best 
applied  to  these  cylindrical  shafts  in  limestone 
districts. 

The  water,  after  forming  a  "  swallow  -  hole "  to 
some  depth,  may  reach  a  well  -  marked  plane  of 
stratification,  along  which  it  can  penetrate,  causing 
solution  of  the  limestone  along  that  plane,  and 
giving  rise  to  a  cave.  It  will  eventually  issue  at 


154    SCIENTIFIC   STUDY   OF   SCENERY 


the  side  of  a  valley,  where  the  bedding  plane  reaches 
the  surface,  as  illustrated  in  Fig.  34,  where  5  is  shale, 
L  limestone,  in  which  the  joints  are  represented  by 
nearly  vertical,  the  bedding  planes 
by  nearly  horizontal,  lines,  and  V 
is  a  valley.  The  portions  worn 
away  by  the  water  are  indicated 
by  black,  c  being  caves,  and  sh 
swallow-holes.  The  swallow-hole 
formed  at  the  junction  of  the  upper 
shale  with  the  limestone  may  work 
as  far  as  /,  and  then  along  the 
bedding  plane  from  /  to  2.  If  at 
2  it  meets  with  another  well- 
marked  fissure,  it  may  form  another 
swallow-hole  here,  and  proceed 
along  a  lower  plane  of  bedding  to 
j,  where  it  appears  at  the  surface. 
In  time  a  swallow-hole  may  be 
formed  at  4.,  and  worked  down  to 
the  junction  with  the  lower  shale 
until  the  water  reaches  the  valley, 
when  the  upper  portion  of  the 
cavern  between  j  and  4.  will  be  left 
dry.  At  a  later  period  a  swallow- 
hole  may  be  formed  at  5,  and  so 
on,  and  eventually  the  original 
swallow-hole  will  be  deepened  until 
it  reaches  the  junction  between 
limestone  and  shale,  and  the  cavern 
will  extend  along  this  junction,  the 
upper  caverns  and  many  of  the 
swallow -holes  being  deserted  by 
the  water. 


VALLEYS  155 

The  cross-section  of  the  cavern  will  vary.  The 
floor  will  probably  be  occupied  by  a  stream  which 
forms  a  bed  by  mechanical  erosion,  but  the  main 
portion  of  the  cavern  may  be  determined  by  the 
solubility  of  a  particular  stratum  of  limestone,  which 
is  greater  than  that  of  the  overlying  and  under- 
lying stratum,  and  fragments  of  the  limestone  may  be 
detached  from  the  sides  along  dominant  joints,  and 
from  the  top  along  a  dominant  plane  of  bedding, 
when  the  cave  will  possess  a  roughly  rectangular 
cross-section.  When  the  water  percolates  through 
important  joints  in  the  roof,  these  joints  may  be 
dissolved  where  the  water  hangs,  thus  producing 
dome-shaped  expansions  of  the  cave  along  these 
joints,  as  seen  at  x  of  the  figure.  Sometimes  a 
considerable  portion  of  the  roof  may  fall  in,  as  at  y, 
producing  a  shaft  like  a  swallow- hole  of  gigantic 
proportions ;  such  is  the  huge  Helln  Pot,  on  the 
west  side  of  Ribblesdale,  in  Yorkshire ;  and  by  a 
continuation  of  this  process  and  the  removal  of  the 
fallen  rocks  of  limestone  the  cave  may  be  converted 
into  a  ravine.  This  is  the  origin  of  many  of  the 
ravines  occupying  the  sides  of  our  limestone  uplands. 
From  the  sides  of  lateral  caverns  streams  may  pour 
into  these  huge  shafts  formed  by  the  subsidence 
of  the  roof,  as  shown  in  Weathercote  Cave,  near 
Ingleton. 

The  beauty  of  the  interior  of  limestone  caverns 
is  largely  due  to  the  formation  of  stalactites  and 
stalagmite  within  them.  The  formation  of  a  stalac- 
tite is  well  seen  on  the  under-side  of  many  bridges ; 
the  water  which  percolates  through  the  masonry 
dissolves  some  of  the  lime  of  the  mortar,  and  when 
it  reaches  the  air  redeposits  it  in  pendent  masses 


156     SCIENTIFIC   STUDY   OF   SCENERY 

like  icicles.  The  process  as  seen  in  the  cavern  is 
as  follows  : — Water  percolates  along  a  joint  and  dis- 
solves some  lime;  when  it  reaches  the  roof  of  the 
cave  the  water  is  suspended  as  a  drop,  and  this 
evaporates  on  the  exterior,  and  a  little  film  of  lime 
is  deposited  as  a  ring  round  the  drop,  being  pre- 
vented from  forming  at  the  bottom  by  the  movement 
of  the  water.  The  next  drop  hangs  to  this  ring,  and 
a  further  ring  is  formed  in  continuation  of  the  first ; 
and  so  the  process  goes  on,  till  a  long,  pellucid,  straw- 
like  tube  hangs  from  the  roof.  Sooner  or  later  the 
interior  of  this  tube  becomes  blocked,  and  the  water 
trickles  down  the  outside,  causing  the  formation  of 
coat  after  coat  of  lime,  until  the  stalactite  exists 
as  a  thick  cylindrical  or  conical  pendent  mass.  In 
the  meantime  drops  fall  on  the  floor  beneath  the 
stalactite,  undergo  further  evaporation  there,  and 
form  deposits  of  stalagmite  in  sheets  or  bosses. 
The  wall  of  the  cavern  is  also  bathed  with  moisture 
in  places,  and,  owing  to  the  evaporation  of  this, 
masses  of  stalagmite  swathe  the  sides  of  the  cavern 
like  folds  of  drapery.  As  the  formation  of  stalactites 
is  mainly  limited  to  the  joint-planes  they  are  often 
found  running  in  linear  series  approximately  at  right 
angles  to  one  another,  and  as  the  direction  of  the 
cavern  is  probably  determined  by  the  same  joints,  one 
set  will  be  parallel  to  the  length  of  the  cavern,  and 
the  other  will  run  across  it.  In  the  accompanying 
plate,  from  a  photograph  of  a  portion  of  the  Ingle- 
borough  Cave  at  Clapham,  in  Yorkshire,  taken  by 
Mr.  G.  Towler,  and  reproduced  by  his  permission,  the 
formation  of  stalactites  and  stalagmite  is  well  shown. 
As  caverns  are  liable  to  destruction  by  further 
operation  of  the  cause  which  produced  them — namely, 


VALLEYS  157 

water  denudation — and  as  the  materials  which  are 
washed  into  caves  tend  to  accumulate  there,  while 
the  lime  which  is  carried  in  solution  is  deposited  as 
stalactite  and  stalagmite,  and  the  cave  may  be 
eventually  filled  up  by  material  deposited  from 
solution,  it  is  evident  that  caves  cannot  be  very 
long-lived,  and  that  all  existing  caves  must  be, 
geologically  speaking,  of  recent  date. 

Before  quitting  consideration  of  caverns  reference 
may  be  made  to  the  remarkable  ice -caverns,  or 
glacieres,  which  are  the  subject  of  a  special  work 
by  the  present  Bishop  of  Bristol.1  These  caves  are 
found  in  several  places,  including  the  limestone 
districts  of  the  Jura  and  the  Pyrenees,  and  are 
remarkable  as  containing  ice  all  the  year  round. 
They  occur  at  high  altitudes,  and  accordingly  the 
air  even  in  summer  is  not  excessively  warm.  They 
are  explained  by  Dr.  Browne  as  follows  :  "  Occurring 
at  a  lower  level  than  the  mouth,  the  ice  formed  in 
winter  is  kept  from  melting  to  any  extent  in  summer 
because  the  warm,  light  air  cannot  displace  the  heavy, 
cold  air  beneath  to  a  considerable  degree,  and  the 
warm  air  which  reaches  the  ice  is  deprived  of  its 
heat  by  the  work  of  melting  a  small  quantity  of  the 
ice,  leaving  the  remainder  to  occupy  the  floor  of  the 
cave  throughout  the  summer." 

1  Ice-caves  in  France  and  Switzerland,  by  Rev.  G.  F.  BROWNE  (1865). 


CHAPTER   XL 

LAKES 

THE  study  of  lakes  has  received  very  consider- 
able attention  during  recent  years.  The  great 
works  of  Forel  on  Geneva1  and  of  A.  Delabecque 
on  the  lakes  of  France 2  have  stimulated  geographers 
to  follow  the  pursuit  of  limnology,  and  in  our  own 
country  the  accurate  and  careful  observations  of 
Mill  on  the  lakes  of  English  Lakeland3  have 
supplied  the  student  of  scenery  with  much  valuable 
material. 

The  existence  of  any  hollow  which  is  capable  of 
retaining  a  considerable  sheet  of  inland  water  may 
give  rise  to  a  lake,  and  as  the  requisite  hollows  may 
be  formed  in  various  ways,  lakes  may  and  do  present 
considerable  diversity  of  features. 

We  may  commence  with  consideration  of  the  con- 
ditions which  may  produce  a  lake.  Granted  that  the 
requisite  hollow  exists,  the  formation  and  character 
of  the  lake  depends  upon  climatic  conditions.  In  an 
arid  climate  the  hollow  may  be  waterless,  or  if  the 
rainfall  is  small,  the  bottom  of  the  hollow  may  be 
occupied  by  a  lake  having  no  outlet,  whereas  if  the 
rainfall  be  sufficient  to  fill  the  hollow  to  the  height  of 

1  FOREL,  F.  A.,  Le  Uman. 
*  DELABECQUE,  A.,  Les  Lacs  Fran$ais. 
3  MILL,  H.  R.,  The  English  Lakes. 
158 


LAKES  159 

the  lowest  part  of  its  rim  an  outflow  will  be  estab- 
lished. The  physical  characteristics  of  the  lakes  of 
desert  regions  which  depend  upon  climate  will  be 
discussed  when  we  consider  the  features  of  those 
regions,  and  we  shall  here  consider  the  conditions 
which  are  necessary  for  the  formation  of  the  hollows 
requisite  for  the  accumulation  of  the  waters  of  lakes. 

A  hollow  adapted  for  the  retention  of  water  may 
be  formed  in  four  ways  :  (i)  by  accumulation  of 
material  above  the  existing  surface  of  the  earth  to 
form  a  barrier  or  dam  ;  (ii)  by  differential  move- 
ment of  a  portion  of  the  earth's  crust ;  (iii)  by 
volcanic  action  forming  craters ;  (iv)  by  erosion. 

(i)  Lakes  formed  by  accumulation  of  material  are 
very  widely  distributed,  and  the  material  which  forms 
the  barrier  or  dam  may  be  accumulated  under  very 
different  conditions.  In  some  cases  the  barrier  may 
completely  surround  the  hollow,  as  when  the  lake 
exists  owing  to  unequal  accumulation  of  extensive 
sheets  of  material.  Such  lakes  are  often  found  exist- 
ing in  the  hollows  of  glacial  drift,  and  are  termed 
"  kettle-holes  "  by  American  geologists.  According 
to  the  late  Professor  Carvell  Lewis,  the  meres  of 
Cheshire  are  of  this  character.  Small  pools,  many 
of  which  are  dried  up  in  times  of  drought,  are 
frequently  found  among  the  moraine  mounds  of  our 
upland  regions  ;  they  usually  present  few  features 
of  interest  in  themselves,  though  they  are  often 
effective  as  a  foreground  to  mountain  views.  The 
little  Schwarz  See  at  Zermatt  occupies  a  hollow  in 
moraine  material,  and  its  immediate  surroundings 
are  tame,  but  the  view  of  the  Ober-Gabelhorn  as 
seen  from  the  end  opposite  the  little  chapel  is  very 
impressive.  (See  plate.) 


160    SCIENTIFIC   STUDY   OF   SCENERY 

When  a  region  has  been  recently  raised  above 
sea-level,  lakes  may  be  formed  in  inequalities  of  the 
former  sea-floor. 

Again  we  may  find  the  barrier  blocking  the  stream 
of  a  valley,  and  giving  rise  to  a  lake  which  drains 
over  the  barrier,  but  unless  the  barrier  is  prolonged 
for  some  distance  down  the  valley,  or  is  composed 
of  hard  rock,  lakes  of  this  character  are  apt  to  be 
short-lived,  for  the  water  issuing  from  the  lake  erodes 
the  barrier,  and  the  lake  is  drained.  At  other  times 
the  water  runs  between  the  barrier  and  the  original 
surface  slope,  and  a  barrier  of  this  nature  is  also 
readily  destructible.  If  the  barrier  be  raised  to  a 
sufficient  height,  the  lake  level  may  be  raised  so 
that  the  water  reaches  a  col  which  is  at  a  lower 
level  than  the  lowest  part  of  the  barrier,  and  lakes  of 
this  nature  will,  from  the  circumstances  of  the  case, 
be  much  more  permanent  than  those  which  have 
an  outlet  over  a  dam  of  more  or  less  incoherent 
material. 

We  may  now  consider  the  nature  of  the  material 
which  may  accumulate  to  form  a  dam  sufficient  to 
give  rise  to  a  lake.  In  the  first  place,  we  may  take 
the  case  of  ice,  for  though  an  icy  dam  is  naturally 
unstable,  ice-barred  lakes  present  many  features  of 
interest.  Avalanches  of  ice  falling  from  the  terminal 
cliff  of  a  glacier  may  accumulate  across  a  valley 
bottom  to  form  a  dam,  which  will  allow  the  waters 
of  a  temporary  lake  to  collect  above  it,  as  happened 
in  1818  in  the  valley  of  the  Dranse,  which  was 
blocked  by  ice  fragments  falling  from  the  Getroz 
glacier,  giving  rise  to  a  lake,  the  subsequent  bursting 
of  which  caused  a  disastrous  flood  in  the  Rhone 
valley.  At  the  junction  of  two  glaciers  a  hollow 


1 62     SCIENTIFIC   STUDY   OF   SCENERY 

some  miles  in  length,  is  situated  in  a  valley  stopped 
at  both  ends  by  ice ;  and  to  the  north  of  the  same 
glacier  another  valley  is  not  only  blocked  by  ice  at 
its  lower  end,  but  a  tongue  of  ice  flows  over  a  col 
in  the  centre  and  splits  the  lake  into  two,  separated 
by  a  mass  of  ice.  Further  north  are  several  large 
lakes,  one  apparently  about  fifteen  miles  long,  which 
are  blocked  at  their  lower  ends,  and  the  water  flows 
to  the  sea  over  cols  situated  at  the  heads  of  the 
valleys.  The  terraces  formed  by  these  lakes  may 
form  conspicuous  objects  in  the  landscape  when  the 
ice  has  vanished.  It  is  well  known  that  many 
writers  have  advocated  the  formation  of  the  famous 
Parallel  Roads  of  Glen  Roy  in  this  manner. 

In  Alaska  some  of  the  glaciers  are  in  a  very 
peculiar  condition,  which  will  be  more  fully  con- 
sidered in  the  chapters  devoted  to  the  scenic  effects 
of  ice.  One  of  the  results  of  this  condition  is,  that 
the  ice,  while  moving  down  the  valleys,  receives  no 
addition  from  snow-fields  at  the  head,  and  accord- 
ingly the  tops  of  the  valleys  are  free  of  ice.  This 
is  seen  in  some  of  the  valleys  which  slope  down  to 
the  Muir  glacier,  and  the  upper  parts  of  these  valleys 
are  occupied  by  lakes,  which  are  supported  by  the 
barrier  of  ice  below.  Berg  Lake,  formed  in  this 
way,  is  four  miles  long ;  and  Main  Lake,  which  runs 
across  Main  Valley,  has  a  length  of  about  seven 
miles.1 

In  passing  to  the  consideration  of  more  permanent 
barriers,  we  may  commence  with  one  of  the  most 
durable,  namely,  lava  poured  out  from  a  volcano,  and 
crossing  a  valley,  as  described  in  the  case  of  the 

1  GUSHING,  H.  P.,  "Notes  on  the  Muir  Glacier  Region,  Alaska," 
Amer.  Geologist,  October,  1891. 


LAKES  163 

river  Simeto.  It  is  obvious  that  the  drainage  may 
be  ponded  back  by  the  barrier,  and  a  lake  formed. 
M.  Delabecque,  in  his  work  on  the  lakes  of  France, 
mentions  one  or  two  lakes  which  were  formed  in 
this  manner,  including  the  Lac  d'Aydat,  near  Cler- 
mont-Ferrand, dammed  by  a  basaltic  flow  from  the 
Puy  de  Lassolas.  In  rare  cases  a  volcano  may 
actually  be  formed  at  the  bottom  of  a  valley  in  such 
a  position  as  to  form  a  dam.  Two  possible  cases  are 
cited  and  figured  by  Delabecque,  namely,  the  case  of 
Lake  Chambon,  near  Clermont-Ferrand,  and  that  of 
Montcyneire. 

The  remaining  barriers  to  be  considered  are  formed 
by  the  accumulation  of  more  or  less  incoherent 
material,  and  accordingly,  as  above  stated,  the  lakes 
are  usually  short-lived,  unless  the  barrier  is  so  high 
that  the  drainage  is  diverted  over  a  col  formed  of 
harder  rock. 

Landslips  may,  and  often  do,  give  rise  to  lakes, 
for  the  amount  of  material  is  often  so  great,  and  the 
barrier  is  formed  so  suddenly,  that  the  stream  has 
no  time  to  keep  a  passage  open  during  the  formation 
of  the  barrier.  It  may  be  remarked  in  this  place 
that  the  lakes  formed  by  incoherent  barriers,  and 
having  their  exits  over  the  barriers,  often  have  a 
longer  existence  than  they  would  otherwise  have, 
because  the  sediment  of  the  river  is  deposited  in  the 
lake,  and  the  issuing  stream,  being  deprived  of  sedi- 
ment, is  incapable  of  producing  much  corrasion  in 
a  short  time  even  if  its  bed  be  composed  of  more  or 
less  incoherent  materials.  The  Lake  of  Derborence, 
to  the  north-west  of  Sion,  in  the  upper  part  of  the 
Rhone  valley,  is  a  good  example  of  a  lake  formed 
by  a  landslip.  It  came  into  existence  in  1749  as 


1 64    SCIENTIFIC   STUDY   OF   SCENERY 

the  result  of  a  landslip  from  the  Diablerets,  and  is 
blocked  by  a  dam  composed  of  huge  angular  frag- 
ments. 

Near  the  sea-shore  extensive  sheets  of  water  are 
often  formed  by  the  formation  of  barriers  composed 
of  beach  deposit  or  blown  sand.  On  the  Atlantic 
and  Mediterranean  coasts  of  France  a  number  of 
shallow  lakes  and  lakelets  exist,  known  as  etangs, 
some  of  which  are  due  to  beach  barriers,  others  to 
dams  of  blown  sand,  and  some,  as  shown  by  Dela- 
becque,  belong  to  a  different  class,  being  caused 
to  a  large  extent  by  subterranean  solution.  He 
mentions  the  Jiangs  of  Kerloch  and  Kergalan,  on  the 
Atlantic  coast,  and  all  those  situated  between  Cape 
Bear  and  the  Etang  de  1'Estomac,  as  well  as  that 
of  Pesquiers,  near  Hyeres,  as  being  due  to  barriers 
of  beach,  while  several  on  the  coast  of  Morbihan, 
and  all  those  between  the  Pointe  de  Grave  and  the 
"  falaises "  of  Biarritz,  are  due  to  barriers  of  blown 
sand.  The  actual  origin  of  these  barriers,  composed 
of  sea-beach  and  sand-dune,  will  be  considered  in 
later  chapters. 

River  deposits  of  organic  and  inorganic  origin  may 
form  barriers  which  hold  up  lakes.  Sir  A.  Geikie 
records  the  work  of  the  beaver,  which  "  by  cutting 
down  trees  (sometimes  one  foot  or  more  in  diameter) 
and  constructing  dams  with  the  stem  and  branches 
checks  the  flow  of  watercourses,  intercepts  floating 
materials,  and  sometimes  even  diverts  the  water  into 
new  channels.  This  action  is  typically  displayed  in 
Canada  and  in  the  Rocky  Mountain  regions  of  the 
United  States.  Thousands  of  acres  in  many  valleys 
have  been  converted  into  lakes."1 

3  GEIKIE,  Sir  A.,  Text-book  of  Geology,  3rd  edition,  p.  474. 


LAKES  165 

The  formation  of  crescentic  lakes  owing  to  wind- 
ing rivers  in  an  alluvial  plain,  forming  "cuts-off" 
and  leaving  the  old  windings  as  lakes  and  pools,  was 
described  in  Chapter  IX.  It  is  to  be  noted  that  the 
water  occupied  its  position  before  the  formation  of 
the  barrier.  The  same  is  the  case  with  the  "  broads  " 
of  Norfolk,  whose  origin  is  somewhat  similar,  though 
more  complex.  Their  formation  has  been  described 
by  Dr.  J.  W.  Gregory,  and  a  reference  to  the  litera- 
ture of  the  subject  will  be  found  at  the  end  of  his 
paper.1  He  gives  reason  to  suppose  that  the  East 
Anglian  rivers  once  opened  into  large  estuaries  like 
those  of  the  Tees,  Tyne,  Thames,  and  the  Wash  and 
H umber.  Owing  to  the  peculiar  tidal  movement  off 
the  East  Anglian  coast,  which  comes  from  the  north 
through  a  narrowing  sea,  the  sediment  is  piled  up  by 
the  tides  on  the  north  side  of  the  mouths  of  the  East 
Anglian  rivers,  and  forms  breakwaters,  by  which  the 
force  of  the  current  of  the  rivers  is  checked,  and  they 
deposit  their  load  of  material  against  the  inner  side 
of  these  breakwaters,  thus  causing  the  estuaries  to 
become  silted  up  from  their  seaward  terminations, 
instead  of  at  the  head  only.  This  tract  of  silt  "would, 
by  the  continuation  of  these  operations,  work  its  way 
gradually  backward  up  the  estuary,  leaving  a  great 
sheet  of  water  separated  from  the  sea  by  a  bank  of 
alluvium  ;  of  this  Breydon  Water  may  be  the  dimi- 
nished representative.  But  as  the  land  worked  further 
backward  it  would  cross  the  entrance  of  branches  of 
the  estuary;  the  sediment  would  be  carried  along 
the  central  channel,  upon  the  sides  of  which  it  would 
be  deposited ;  it  could  thus  cut  off  the  branches 
either  entirely,  as  in  the  case  of  Fritton  Lake,  or 
1  GREGORY,  J.  W.,  Natural  Science,  vol.  i.  (1892),  p.  347. 


1 66     SCIENTIFIC   STUDY   OF   SCENERY 

connected  by  a  channel  just  sufficient  for  the  escape 
of  the  surplus  rainfall,  as  does  the  memorable  Muck 
Fleet  for  the  three  great  sheets  of  Rollesby,  Ormesby, 
and  Filby  Broads."  The  barriers  are  increased  and 
compacted  by  the  abundant  growth  of  marsh  vegeta- 
tion upon  them. 

Dr.  Gregory  also  points  out  that  those  broads  which 
lie  along  the  courses  of  the  main  rivers  are  more 
complicated.  One  large  broad  is  formed  at  first,  and 
the  main  river  forms  a  delta  at  its  entrance.  This 
delta  grows  outward  along  the  course  of  the  river, 
the  sediment  being  strained  off  by  the  vegetation 
which  grows  on  the  banks  formed  on  either  side  of 
the  current.  By  degrees  this  barrier  is  formed  right 
across  the  original  broad,  dividing  it  into  two,  and 
the  process  of  subdivision  may  take  place  more  than 
once.  In  this  way  he  accounts  for  the  formation  of 
Wroxham  Broad,  and  of  six  other  broads  to  the 
east  of  it,  along  the  course  of  the  river  Bure,  all 
having  been  formed  by  the  subdivision  of  one 
original  large  broad. 

In  the  case  of  upland  streams,  lakes  and  tarns  may 
be  formed  by  the  deposition  of  a  delta  by  one  stream 
where  it  enters  another,  if  the  main  stream  has  not 
sufficient  volume  to  carry  away  the  sediment  brought 
by  the  tributary.  Anyone  who  has  walked  from 
Borrowdale  to  Wastdale,  in  the  Lake  District,  over 
the  Sty  Head  Pass,  will  remember  a  small  tarn,  Sty 
Head  Tarn,  near  the  head  of  the  pass  on  the  Borrow- 
dale side  (see  plate).  It  is  barred  by  a  delta  descending 
from  the  two  Gables,  and  as  the  small  stream  into 
which  it  flows  has  no  great  volume,  it  has  been 
unable  to  carry  away  the  material  brought  down  the 
Gables'  slope,  and  the  accumulated  delta  has  driven 


LAKES  167 

the  main  stream  some  way  back  and  formed  a 
barrier,  which  holds  up  the  tarn,  the  waters  from 
which  now  escape  by  a  channel  running  between  the 
margin  of  the  delta  and  the  solid  rock  on  the  other 
side.  Lakes  may  be  formed  in  this  manner  on  a 
fairly  large  scale,  especially  when  the  upper  waters 
of  the  main  river  are  deflected  by  beheading,  and 
accordingly  the  stream,  owing  to  diminished  volume, 
loses  much  of  its  transporting  power. 

It  may  be  stated  here  that  these  deltaic  barriers 
may  in  mountain  regions  resemble  moraines  so 
closely  that  it  requires  considerable  care  to  dis- 
tinguish them.  The  late  Professor  J.  D.  Forbes1 
writes  : — 

"Between  St.  Nicholas  and  Randa  several  wild  and 
bridgeless  torrents  have  to  be  crossed,  which,  in  bad 
weather,  must  make  this  route  nearly  impassable.2  I 
noticed  particularly  the  mode  in  which  a  violent  torrent 
accumulates  boulders,  forming  a  mound  of  blocks  on  either 
hand,  which  serves,  in  some  measure,  to  restrain  its  fury, 
whilst  the  level  of  its  bed  is  continually  raised  by  the 
detritus  which  it  accumulates ;  and  when,  by  extraordinary 
freshes,  the  barrier  is  broken,  the  country  on  either  side 
is,  of  course,  deluged.  I  only  speak  now  of  the  wildest 
and  most  powerful  torrents  descending  at  a  great  angle, 
and  which  act  sufficiently  on  blocks  to  roll  them  with  the 
aid  of  gravity  for  a  great  way,  and  chafe  them  into 
irregularly  rounded  masses,  with  a  noise  which  everyone 
who  has  visited  the  Alps  recalls  as  one  of  the  most  striking 
of  natural  sounds,  accompanied,  as  it  always  is,  with  an 
impression  of  irresistible  force.  Now,  these  rocky  accumu- 
lations have  a  very  striking  resemblance  to  the  moraines  of 

1  FORBES,  J.  D.,  A  Tour  of  Mont  Blanc  and  Monte  Rosa,  p.  237. 
8  This  was  written  in  1855. 


1 68     SCIENTIFIC   STUDY   OF   SCENERY 

glaciers,  and  this  is  a  circumstance  which  it  is  well  to  be 
aware  of,  and  which  has  not,  I  think,  been  prominently 
stated.  In  form  these  mounds  resemble  moraines,  the 
external,  and  even  the  internal  slope,  being  in  both  cases 
usually  determined  by  the  angle  of  repose  of  the  blocks. 
The  materials  of  both  are  also  alike; — angular  blocks,  more 
or  less  rounded  by  friction,  never  quite  smoothed  or 
polished,  angular  gravel,  and  sharp  sand.  In  the  dis- 
position of  the  materials  I  have  not  observed  that  regularity 
of  arrangement  which  is  said  to  distinguish  water  action 
from  that  of  glaciers.  On  the  contrary,  the  deposit  of 
these  torrents  seems  to  be  wholly  devoid  of  layers  of 
coarser  or  finer  materials,  and,  as  in  true  moraines,  the 
largest  blocks  often  lie  uppermost.  I  may  mention  the 
great  torrent  descending  from  the  Dent  du  Midi,  which 
devastates  the  country  above  St.  Maurice,  as  another 
example  of  this." 

The  dry  deltas  which  descend  from  mountain 
slopes  only  differ  from  torrent  deltas  in  the  inter- 
mittent character  of  the  water  supply,  and  the  falling 
of  blocks  split  off  by  frost  and  changes  of  tempera- 
ture in  the  dry  season.  They  are  intermediate  in 
character  between  torrent  deltas  and  screes,  and  may 
form  barriers  supporting  lakes  in  the  same  way. 

Screes  also  act  as  barriers  in  the  same  way  if  some 
of  the  material  is  sufficiently  comminuted  to  prevent 
the  water  from  draining  through  the  interstices  be- 
tween the  larger  blocks.  The  tarn  known  as  Goats' 
Water,  on  the  side  of  the  Old  Man  of  Coniston, 
in  the  Furness  district  of  North  Lancashire,  is 
dammed  by  screes,  and  I  may  call  attention  to  two 
other  tarns  formed  in  the  same  way,  which  admirably 
illustrate  the  manner  in  which  a  lake  supported  by 
a  barrier  may  have  its  drainage  diverted  from  the 


HAWESWATER 


LAKES  169 

barrier,  so  that  it  ultimately  drains  over  bare  rock. 
One  is  situated  in  Ruthwaite  Cove,  a  recess  of 
Helvellyn,  and  is  known  as  Hard  Tarn.  It  is  quite 
small  and  extremely  shallow,  but  is  surrounded  by 
solid  rock  on  all  sides  except  at  the  main  exit,  which 
runs  over  a  barrier  of  screes  which  has  formed  the 
tarn.  The  water  now  stands  at  such  a  height  that  in 
wet  weather  the  water  level  stands  just  above  a  low 
depression  in  the  rock,  and  accordingly  there  is  here 
a  wet-weather  exit,  along  which  a  groove  is  being 
cut  by  the  water.  As  the  growth  of  the  screes 
increases,  the  scree  exit  will  be  the  wet -weather 
exit,  and  the  normal  exit  will  be  over  the  solid  rock, 
a  state  of  things  actually  found  in  the  tiny  Ffynnon 
Freeh,  in  Cwm  Glas,  on  Snowdon,  as  described  by 
Mr.  W.  W.  Watts.1  The  exit  of  each  of  these  tarns 
will  ultimately  abandon  the  dam,  and  exist  perma- 
nently over  the  solid  rock,  an  event  which  has 
happened  in  the  case  of  a  large  number  of  similar 
tarns  and  lakelets. 

In  many  mountain  regions  the  cwms  and  corries 
are  occupied  by  great  snow-slopes  during  the  winter 
months.  The  fragments  split  from  the  cliffs  above 
by  the  action  of  the  frost  come  flying  down  the 
slopes,  and  form  a  crescentic  barrier  around  the 
mouth  of  the  cwm,  which  may  hold  up  the  water  to 
form  a  tarn.  Similar  slopes  on  the  sides  of  a  hill 
may  block  a  valley  just  as  a  delta  or  slope  of  screes 
does.  The  little  tarn  of  Smallwater  near  Haweswater, 
in  Lakeland,  shown  in  the  plate,  seems  to  be  due  to 
this  cause,  and  its  exit  is  now  permanently  over  solid 
rock,  with  the  somewhat  remarkable  consequence  that 

1  WATTS,   W.  W.,   "Notes  on  some  Tarns  near  Snowdon,"  Rep. 
Brit.  Assoc.  for  1895,  p.  683. 


1 70    SCIENTIFIC   STUDY   OF   SCENERY 

the  bottom  of  the  original  valley  below  the  dam  is 
dry,  and  the  present  stream  below  the  exit  runs  for 
some  distance  in  a  shallow  groove  cut  into  the  rock 
of  the  hill-side  some  height  above  the  valley  bottom. 

We  must  now  consider  the  barriers  formed  of 
glacial  drift,  which  are  the  most  important  of  the 
many  barriers  due  to  accumulation  of  material  across 
a  valley.  A  great  number  of  lakes  and  tarns  at 
home  and  abroad  owe  their  existence  to  a  barrier 
of  this  nature.  I  may  mention  Codale  and  Easedale 
Tarns  near  Grasmere,  Devoke  Water  between  Esk- 
dale  and  the  Duddon  valley,  Burnmoor  Tarn  and 
Sprinkling  Tarn  on  Scawfell,  Red  Tarn  and  Keppel- 
cove  Tarn  on  Helvellyn,  in  Lakeland ;  Llyn  Goch, 
Llyn  Glas,  and  Llyn-y-nadroedd  on  the  west  side 
of  Snowdon,  and  Llyn  d'ur  Arddu  on  its  north-west 
side,  in  North  Wales.  Of  larger  lakes,  Windermere, 
Bassenthwaite,  Ullswater,  and  Thirlmere  in  Lake- 
land ;  the  lakes  of  Llanberis,  Gwynant,  and  many 
others,  may  also  be  due  to  great  barriers  of  drift 
extending  far  down  the  valleys.  Delabecque  cites 
a  number  of  French  lakes  formed  by  a  similar 
barrier,  as  the  lakes  of  Chalain,  Chambly,  Nantua, 
and  others  in  the  Jura,  and  Gerardmer,  Longemer, 
Blanchemer,  among  those  of  the  Vosges.  Some  of 
these  lakes  are  produced  by  lateral  moraines,  others 
by  terminal  moraines,  and  others  again  by  the  great 
masses  of  "  drift "  which  spread  over  extensive  tracts 
of  country. 

The  statement  that  lakes  may  be  blocked  by 
terminal  moraines  requires  a  word  of  explanation. 
As  an  extensive  torrent  always  issues  from  the  end 
of  a  glacier,  it  might  be  supposed  that  a  passage 
through  the  barrier  would  always  be  kept  open. 


LAKES  171 

No  doubt  this  is  often  the  case,  but  the  stream  does 
not  always  cut  down  to  the  solid  rock,  for  we  often 
find  it  rushing  over  moraine  material  for  some  distance 
below  the  snout  of  the  glacier,  and  on  the  recession 
of  the  ice  sufficient  moraine  may  be  left  to  form 
a  barrier  supporting  the  waters  of  a  lake,  and, 
secondly,  even  if  the  stream  does  cut  through  solid 
rock,  the  point  of  issue  of  the  stream  need  not  be 
situated  just  over  the  bottom  of  the  original  valley, 
and  here  again  a  barrier  of  moraine  may  occur,  which 
gives  rise  to  a  lake. 

The  most  striking  tarns  are  those  formed  by  a 
dam  of  moraine  at  the  mouth  of  a  cwm,  the  com- 
bination of  lakelet  and  mural  precipice  being  often 
extremely  picturesque.  The  finest  tarn  in  the  Lake 
District,  Bleawater  Tarn,  near  Haweswater,  forms 
a  nearly  complete  circle.  The  outer  semicircle  is 
bordered  by  the  retaining  dam  of  moraine,  while 
the  inner  one  is  formed  by  the  fine  cliffs  which  rise 
almost  straight  from  the  shores  of  the  tarn,  and  tower 
up  many  hundreds  of  feet  to  the  ridge  of  High 
Street. 

Those  lakes  which  were  formed  by  drift,  where  the 
exit  was  over  the  original  valley  bottom,  are  usually 
drained  quickly,  as  previously  observed,  and  their 
sites  marked  by  peat  mosses,  and  the  number  of 
these  moss-covered  tracts  in  upland  districts  proves 
that  the  tarns  and  lakelets  which  survive  are  but 
a  small  proportion  of  those  which  once  existed. 
Of  lakes  blocked  by  drift,  of  which  the  exit  is 
now  over  solid  rock,  we  may  mention  Burnmoor 
Tarn,  Codale  Tarn,  Small  Water,  and  Harrop  Tarn 
in  the  Lake  District,  and  of  larger  lakes  Winder- 
mere  and  Bassenthwaite.  Delabecque  has  shown 


i;2     SCIENTIFIC   STUDY   OF   SCENERY 

that  Longemer,  in  the  Vosges,  has  a  similar 
structure. 

A  word  of  explanation  concerning  the  character 
of  the  drift-filled  valleys  is  necessary.  In  many 
cases  they  are  wide  as  compared  with  their  depth, 
but  in  others  we  meet  with  depressions  occupied 
by  drift  at  the  surface,  which  are  narrow  and 
tortuous,  and  if  they  are  filled  with  drift  to  the 
bottom,  which  is  necessary  in  order  that  lakes 
may  be  formed  by  them,  the  drift  must  be  very 
deep ;  a  depth  of  two  or  three  hundred  feet  is 
often  necessary.  The  existence  of  such  drift-filled 
depressions  may  seem  unlikely,  but  it  must  be  re- 
membered that  in  a  glaciated  region  the  waters  of 
the  streams  issuing  from  the  glacier  are  charged  with 
abundance  of  minute  angular  particles  of  sediment, 
which  are  capable  of  cutting  like  a  file,  and  these 
rivers  must  produce  great  vertical  corrasion.  Accord- 
ingly we  frequently  find  that  the  valleys  which  have 
been  occupied  by  ice  comparatively  recently  are  wide 
where  the  ice  has  recently  receded,  but  that  lower 
down  the  rivers  which  flow  from  the  glaciers  drain 
through  extremely  narrow  gorges  cut  out  by  the 
streams,  to  which  Desor  has  given  the  name  roflas. 
The  gorge  of  the  Trient,  near  Vernayaz,  in  the  Upper 
Rhone  valley,  is  an  example  ;  and  many  others 
occur. 

If  ice  passed  over  these  gorges,  they  would  readily 
become  filled  with  drift,  especially  if  the  ice  moved 
transversely  to  their  general  direction,  and  when 
filled  up  their  detection  might  be  a  matter  of  some 
difficulty. 

There  is  one  particular  case  in  which  glacial  drift 
may  produce  a  barrier  under  somewhat  exceptional 


LAKES  173 

circumstances  which  must  be  noticed.  It  has  been 
seen  that  much  of  the  drainage  in  a  limestone  region 
is  subterranean.  Suppose  a  stream  to  fall  down  a 
swallow-hole.  The  stream  above  the  swallow -hole 
will  erode  its  channel  and  gradually  lower  it,  and 
if  the  swallow-hole  should  slant  downwards,  a  portion 
of  the  limestone  above  it  may  become  engulfed. 
Eventually  the  stream  will  fall  into  the  hole  at  some 
distance  below  the  general  level  of  the  surface.  If 
the  swallow -hole  be  partly  or  entirely  rilled  up  in 
any  way,  the  subterranean  drainage  may  be  stopped 
or  checked  to  such  an  extent  that  the  whole  of  the 
water  cannot  be  carried  underground,  when  it  will 
accumulate  in  the  old  channel  to  form  a  lake,  until 
it  reaches  a  level  at  which  it  can  overflow.  M. 
Penck  has  suggested  that  in  regions  which  were 
formerly  glaciated  the  orifice  may  be  stopped  with 
impermeable  morainic  material,  forming  a  barrier. 
In  this  manner  M.  Delabecque  explains  the 
formation  of  the  remarkable  Lake  Chaillexon, 
forming  a  part  of  the  course  of  the  Doubs,  in  the 
Jura,  which  is  shown  in  Figs.  49,  53,  and  104  of 
his  work  on  the  French  lakes,  while  a  plan  is 
given  in  Plate  VII.  The  lake  is  deepest  at  its  lower 
end,  where  a  submerged  swallow-hole  having  a  depth 
of  31^  metres  occurs.  The  lake  itself  is  sinuous 
in  form,  its  banks  rising  in  precipices  of  limestone 
on  either  side,  with  the  corresponding  beds  easily 
recognisable  in  each  precipitous  cliff. 

It  is  clear  that  the  blocking  of  the  swallow-hole 
by  drift  is  not  essential  to  the  formation  of  a  lake 
in  a  region  of  fissured  limestone ;  if  the  swallow-hole 
in  any  way  becomes  too  small  to  allow  the  whole 
of  the  drainage  to  be  carried  away  underground,  a 


174     SCIENTIFIC   STUDY   OF   SCENERY 

lake  will  result,  though  glacial  drift  is  likely  to 
form  the  most  efficient  plug  in  closing  or  partially 
closing  the  orifice. 

(ii)  Lakes  formed  by  differential  movement  of  por- 
tions of  the  earth's  crust  may  now  be  considered. 
Before  discussing  the  formation  of  lakes  owing  to 
extensive  movements  of  the  earth's  crust,  produced 
by  deep-seated  changes,  we  may  mention  the  origin 
of  certain  lakes  produced  by  sinking  of  the  super- 
ficial portion  of  the  crust  owing  to  the  solution 
and  removal  of  material  beneath.  We  have  already 
taken  into  account  the  action  of  acidulated  water 
upon  limestone  rocks,  and  have  seen  that  one  of  the 
effects  was  the  giving  way  of  the  roofs  of  under- 
ground caverns,  producing  hollows  above.  These 
hollows  would  be  admirably  adapted  for  the  for- 
mation of  lakes  were  it  not  for  the  fissured  nature 
of  the  limestone,  which,  as  a  general  rule,  permits 
the  underground  drainage  of  the  water  which  would 
otherwise  accumulate  in  the  hollow,  and  give  rise  to 
a  lake;  and  accordingly  lakes  formed  by  underground 
solution  and  removal  of  limestone  appear  to  be 
comparatively  rare,  and  lakes  formed  by  solution 
of  material  beneath  the  surface  are  more  frequently 
produced  if  rock-salt  or  gypsum  be  the  material 
removed.  Some  writers  have  referred  the  formation 
of  certain  Cheshire  meres  to  the  solution  of  rock- 
salt,  and  it  is  a  fact  that  the  artificial  removal  of 
this  material  in  the  form  of  brine  by  introduction 
of  water  and  artificial  removal  of  the  brine  by 
pumping  has  caused  serious  subsidence  in  the 
Cheshire  district,  with  occasional  formation  of  sheets 
of  water  in  the  hollows.  Many  writers  have  referred 
the  production  of  various  lakes  in  Switzerland  to 


LAKES  175 

underground  solution.  M.  Delabecque  quotes  cases 
of  several  lakes  which  he  considers  to  be  probably 
formed  in  this  manner,  for  instance  the  Lac  de  la 
Girotte,  the  lakes  of  Tipies,  and  the  Lac  du  Mont 
Cenis.  It  is,  of  course,  difficult  to  obtain  definite 
proofs  that  lakes  have  been  formed  in  this  manner, 
as  the  proofs  are  concealed  beneath  the  ground ; 
but  when  lakes  are  found  in  districts  which  are 
known  to  contain  deposits  of  gypsum,  rock-salt, 
or  dolomite,  and  the  origin  of  the  lakes  by  any 
other  process  is  not  indicated,  it  is  legitimate  to 
attribute  them,  with  a  certain  amount  of  probability, 
to  the  solvent  action  of  underground  waters  upon 
the  above-mentioned  salts. 

Mr.  Garwood  has  furnished  me  with  an  illustration 
of  a  lake  the  production  of  which  he  refers  to  under- 
ground solution.  (See  plate.)  This  is  the  Lago  dell' 
Inferno,  at  the  foot  of  the  Tre  Signiori,  a  true 
rock  -  basin  holding  a  lake  about  half  a  mile  in 
length,  and  of  considerable,  though  unknown,  depth  ; 
the  rocky  barrier  round  the  lake  is  well  seen  in  the 
photograph. 

We  now  arrive  at  the  consideration  of  the  lakes 
which  show  evidence  of  existence  owing  to  the 
occurrence  of  those  more  widely  spread  foldings  and 
fractures  of  the  earth's  crust  whose  nature  we  con- 
sidered when  discussing  the  character  of  continental 
and  mountain  uplifts. 

The  differential  movement  which  results  in  bend- 
ing of  the  earth's  crust,  accompanied  by  occasional 
fracture,  is  spoken  of  by  the  American  geologists 
as  "warping,"  the  idea  being  that  the  crust  of  the 
earth  becomes  warped,  just  as  the  cover  of  a  book 
when  held  in  front  of  the  fire.  Now  it  is  clear  that 


176     SCIENTIFIC    STUDY   OF   SCENERY 

if  warping  occurred  in  such  a  way  as  to  cause  the 
bending  up  of  the  portion  of  the  earth's  crust  in  the 
lower  part  of  a  valley,  and  if  the  stream  was  unable 
to  keep  its*  original  channel  open  by  downward 
corrasion,  a  lake  would  be  produced  by  the  process 
of  ponding,  in  the  manner  described  in  the  preceding 
chapter.  It  is  clear  that  there  is  no  a  priori  objection 
to  the  formation  of  lakes  in  this  manner,  and  it 
remains  for  us  to  see  whether  we  have  any  indis- 
putable evidence  of  lake  formation  by  the  ponding 
process. 

One  objection  to  the  extensive  formation  of  lakes 
by  this  process  was  long  ago  made  by  Sir  A.  C. 
Ramsay,  who  pointed  out  that  a  vast  majority 
of  lakes  occur  in  regions  which  can  be  proved  to 
have  been  glaciated  in  geologically  recent  times, 
whereas,  if  a  majority  be  due  to  ponding,  no  such 
connection  should  be  traceable.  We  have  already 
seen  that  the  formation  of  glacial  dams  may  account 
for  many  lakes,  and  the  association  of  lakes  existing 
in  live  rock  basins  and  not  held  up  by  a  dam  of 
accumulation,  with  glacial  phenomena,  was  long  ago 
satisfactorily  explained  by  Lyell,  who  pointed  out 
that  ponding  might  be  prevented  in  ordinary  regions 
by  the  rivers  keeping  their  waterways  open  during 
the  period  of  uplift,  whereas,  if  the  uplifted  tract 
were  covered  by  ice  and  the  latter  were  unable  to 
corrade  to  the  same  extent  as  water,  the  barriers 
could  be  formed,  and  on  the  recession  of  the  ice 
the  rock  basins  would  be  ready  for  the  reception 
of  water  to  form  lakes.1  We  shall  eventually  call 
attention  to  the  evidence  which  has  been  gathered 
during  recent  years  bearing  upon  the  erosive  power 

1  LYELL,  Sir  C.,  Antiquity  of  Man,  4th  edition,  p.  360. 


LAKES  177 

of  ice,  which  points  to  the  comparative  impotence 
of  ice  as  an  erosive  agent. 

No  one  has  ever  seriously  called  into  question  the 
supposition  that  a  large  number  of  the  great  lake 
basins  of  the  world  originated  as  the  result  of 
differential  earth  movement.  Among  the  basins 
which  have  been  formed  in  this  way  are  those  of 
the  Aralo-Caspian  area,  the  Dead  Sea,  the  large 
lakes  of  the  interior  of  Africa,  and  those  which 
occupy  the  Great  Basin  region  of  North  America. 
These  lakes,  though  their  origin  is  generally  similar, 
vary  in  matters  of  detail.  Some  of  the  fresh-water 
lakes  of  Africa  may  have  been  produced  by  con- 
version of  part  of  the  ocean  floor  into  land,  for  Mr. 
Edgar  A.  Smith  has  found  shells  allied  to  marine 
forms  in  the  slightly  brackish  waters  of  Tanganyika, 
while  others  have  probably  been  at  no  time  con- 
nected with  the  ocean,  but  are  due  to  the  formation 
of  basins  by  warping,  the  basins  being  afterwards 
filled  with  fresh  water.  Dr.  Gregory  has  described 
some  of  the  African  lakes  as  occurring  in  a  great 
depression,  bounded  by  steep  parallel  sides,  due  to 
faulting.1  "  From  the  Lebanons  .  .  .  almost  to  the 
Cape  there  runs  a  valley,  unique  both  on  account 
of  the  persistence  with  which  it  maintains  its  trough- 
like  form  throughout  the  whole  of  its  course  of  4000 
miles,  and  also  on  account  of  the  fact  that  scattered 
along  its  floor  is  a  series  of  over  thirty  lakes,  of 
which  only  one  has  an  outlet  to  the  sea."  The 
lakes  of  the  Aralo-Caspian  area  were  undoubtedly 
once  connected  with  the  open  ocean,  and  have  been 
separated  from  it  by  uplift,  for  some  of  them  still 
have  seals  living  in  their  waters,  whereas  we  find 

1  GREGORY,  J.  W.,  The  Great  Rift  Valley  (1896). 
N 


i;8     SCIENTIFIC   STUDY   OF   SCENERY 

evidence  that  the  salt  lakes  of  the  Great  Basin  region 
of  North  America  have  at  no  time  had  any  con- 
nection with  the  ocean.  These  lakes  of  the  Great 
Basin  of  America  are  of  peculiar  interest  on  account 
of  the  very  valuable  detailed  accounts  of  their 
characters  and  origin  which  we  owe  to  the  labours 
of  the  United  States  geological  and  geographical 
surveyors,  and  especially  to  G.  K.  Gilbert  and  I.  C. 
Russell,  whose  monographs  on  the  old  lakes  of 
Lahontan  and  Bonneville  contain  a  host  of  infor- 
mation of  the  greatest  importance  to  the  student 
of  the  earth's  history.1  The  region  of  the  Great 
Basin  extends  from  the  British  possessions  on  the 
north  to  Mexico  on  the  south,  and  though  two  rivers 
traverse  it  on  their  way  to  the  ocean,  the  greater  part 
of  the  area  has  no  drainage  to  the  ocean,  and  is 
occupied  by  barren  tracts  scattered  over  which  are 
salt  lakes.  The  old  lakes  of  Bonneville  and  Lahontan 
have  now  disappeared  owing  to  change  of  climate, 
but  evidence  of  their  former  existence  is  furnished, 
among  other  things,  by  old  lake  shores  at  different 
levels.  Each  of  these  shores  was  naturally  at  a 
constant  level  when  it  was  formed,  but  Gilbert  and 
Russell  have  shown  that  they  have  since  been  bent 
by  warping,  so  that  the  level  of  each  terrace  varies  as 
one  traces  it  laterally,  and  sometimes  the  change  is 
sudden  and  marked  by  a  fault  scarp.  The  upper 
terraces  have  been  deformed  to  a  greater  extent  than 
the  lower  ones,  showing  that  the  process  of  warping 
has  continued  through  long  periods,  and  there  is  no 
doubt  that  the  basin  as  a  whole,  as  well  as  the  two 

1  GILBERT,  G.  K.,  Lake  Bonneville,  and  RUSSELL,  I.  C.,  Geological 
History  of  Lake  Lahontan,  monographs  U.S.  Geol.  Survey,  1890  and 
1885. 


LAKES  179 

great  lakes  which  once  existed  in  it,  whose  history 
has  been  written,  originated  owing  to  the  warping 
action. 

Similar  movements  have  also  occurred  around  the 
great  fresh -water  lakes  of  Canada,  as  shown  by 
Gilbert  and  more  lately  by  Dr.  J.  W.  Spencer,  the 
deformation  of  the  Iroquois  beach  around  Lake 
Ontario  and  of  the  Algonquin  beach  surrounding 
Lake  Huron  being  specially  marked.1  The  origin 
of  the  Canadian  lakes  is,  however,  still  somewhat 
obscure,  as  "great  changes  in  the  drainage  have  been 
produced  by  glacial  interference,  to  such  an  extent, 
indeed,  that  some  writers  have  advocated  the  forma- 
tion of  the  basins  solely  as  the  result  of  the  produc- 
tion of  glacial  dams,  though  most  students  of  these 
lakes  consider  their  existence  to  be  due  to  the  opera- 
tion of  warping  accompanied  by  glacial  interference, 
the  latter  having  caused  diversion  of  drainage. 

The  origin  of  the  Jordan  depression  and  the  Dead 
Sea  is,  as  already  stated,  connected  with  that  of  the 
African  lakes  lying  along  the  line  of  the  Great  Rift. 
Another  fairly  large  lake,  though  a  shallow  one, 
which  has  been  satisfactorily  proved  to  be  due  to 
differential  movement,  is  Lake  Balaton  (the  Flatten 
See),  in  Hungary.2 

The  origin  of  the  great  lakes  which  flank  the  Alps 
has  been  much  discussed,  and  most  writers  are  now 
agreed  that  they  owe  their  existence  chiefly  to  differ- 
ential movement,  though  complications  have  also 
been  produced  by  glacial  interference  with  the  river 

1  SPENCER,  J.  W.,   "Origin  of  the  Basins  of  the  Great  Lakes  of 
America,"  Quart.  Jour.  Geol.  Soc.,  vol.  xlvi.,  p.  523. 

2  An  account  of  this  by  Professor  J.  W.  JUDD  will  be  found  in  the 
Geological  Magazine,  decade  ii.,  vol.  iii.,  p.  5. 


i8o     SCIENTIFIC   STUDY   OF   SCENERY 

drainage.  The  lakes  differ  in  some  respects ;  thus 
Neuchatel,  Bienne,  Morat,  and  the  lower  portion  of 
Geneva  run  parallel  with  the  axis  of  a  great  syncli- 
nal fold  or  trough,  while  Thun  and  Brienz,  Zug, 
Zurich,  Wallensee,  Constance,  Como,  Maggiore, 
Orta,  and  Lugano  occupy  valleys  which  are  trans- 
verse to  the  main  axes  of  folding.  The  transverse 
lakes,  as  pointed  out  by  Heim,  may  be  due  to  the 
sinking  down  of  the  great  mass  of  the  Alps  by 
its  own  weight,  causing  relative  depression  of  the 
heads  of  the  valleys,  though  the  shape  of  Como 
and  Lugano  suggests  that  they  were  formed  in 
valleys  which  once  ran  northward.  Deformation 
of  terraces  has  also  been  noted  in  the  case  of  the 
Alpine  lakes ;  Heim  and  Aeppli  record  them  on 
the  sides  of  Zurich. 

The  existence  of  large  lakes  owing  to  earth  move- 
ment has  been  satisfactorily  proved,  but  it  is  a  matter 
of  considerable  interest  to  inquire  whether  small  lakes 
can  be  produced  in  the  same  manner.  Minor  move- 
ments in  a  direction  transverse  to  a  river  valley  are 
not  likely  to  give  rise  to  lakes  if  they  take  place 
slowly,  ^as  the  rivers  would  keep  their  courses  open, 
unless  indeed  the  valleys  were  occupied  by  ice,  but 
sudden  changes,  such  as  are  productive  of  earth- 
quakes, might  well  cause  the  required  uplift  Mr. 
R.  D.  Oldham  has  observed  cases  of  the  formation 
of  small  rock  basins  which  hold  up  lakes  in  the 
district  affected  by  the  great  Indian  earthquake  of 
June  1 2th,  1897.  These  lakes  occur  in  granite  rocks. 
Through  the  kindness  of  Mr.  Oldham,  I  am  able  to 
reproduce  a  photograph  of  a  lake  formed  during  this 
earthquake.  (See  plate.)  This  particular  lake  (Thirn 
Hat,  Garo  Hills)  is  formed  owing  to  the  existence  of 


LAKES  181 

a  visible  fault,  but  some  smaller  lakes  which  he  has 
observed,  occurring  in  true  rock  basins,  which  were 
formed  during  this  earthquake,  show  no  external 
signs  of  faulting,  as,  for  example,  Naphak,  in  the 
Garo  Hills. 

The  existence  of  small  rock  basins  due  to  earth- 
quake action  is  of  great  importance,  and  the  possi- 
bility of  the  operation  of  earthquakes  should  be 
taken  into  consideration  in  discussing  the  origin  of 
all  lakes,  large  or  small,  which  can  be  definitely 
proved  to  occur  in  basins  margined  by  live  rock 
around  the  entire  sheet  of  water. 

(iii)  Crater  Lakes.  The  formation  of  volcanic 
craters  will  be  described  in  its  proper  place ;  it  is 
sufficient  to  mention  here  that  they  may  be  formed 
as  the  result  of  accumulation,  or  of  explosion,  or 
of  a  combination  of  the  two  processes,  and  when 
the  volcano  is  extinct,  if  the  crater  has  not  been 
breached  or  destroyed,  and  the  material  is  not  too 
porous  to  allow  water  to  accumulate  within  it,  a 
lake  will  be  formed.  Many  well-known  examples 
of  crater  lakes  exist  in  various  parts  of  the  world, 
as  the  Lucrine  lake  and  Avernus  in  the  Phlegraean 
fields  of  Italy,  the  Laacher  See  in  the  Rhenish 
provinces,  Gustavila  in  Mexico,  of  which  a  repre- 
sentation is  given  in  Professor  Judd's  Volcanoes 
(Fig.  72),  and  especially  those  of  Auvergne  and 
Ardeche,  which  are  described  and  illustrated  by 
M.  Delabecque.  Six  of  them  are  shown  in  plan 
on  Plate  XIV.  of  his  work  on  the  lakes  of  France, 
namely,  Lacs  d'Issarles,  du  Bouchet,  de  la  Godi- 
velle  d'en  Haut,  Chauvet,  de  Tazanat,  and  Pavin. 
They  present  a  remarkably  regular  circular  outline, 
and  the  isobaths,  or  lines  of  equal  depth,  are  also 


182     SCIENTIFIC   STUDY   OF   SCENERY 

extremely  regular.  The  largest  of  the  six,  Lac 
dTssarles,  has  a  depth  of  108  metres,  and  the 
comparatively  small  Pavin,  with  a  diameter  of  about 
800  metres,  has  a  depth  of  92  metres.  A  figure 
of  the  Lac  du  Bouchet  is  seen  on  p.  276  of  the 
same  work.  Of  the  Lac  d'Issarles  the  late  Mr. 
G.  P.  Scrope  writes  that  it  is  one  of  those  lakes 
which  "  differ  from  ordinary  craters,  not  only  in  their 
greater  dimensions,  but  in  the  nature  also  and  dis- 
position of  their  enclosure,  which  is  usually  of 
primary  or,  at  all  events,  pre-existing  rocks,  merely 
sprinkled  more  or  less  copiously  with  scoriae  and 
puzzolana,  little,  if  at  all,  elevated  above  the  surface 
of  the  surrounding  country." 

(iv)  Lakes  formed  by  Erosion. — We  now  turn  to 
the  consideration  of  the  formation  of  lakes  by 
processes  concerning  which  there  has  been  a  great 
deal  of  controversy.  The  agents  which  have  been 
suggested  as  capable  of  forming  rock  basins  by 
erosion  of  some  of  the  surface  material  are  wind, 
running  water,  and  ice  in  the  form  of  ice-sheets  and 
glaciers.  According  to  Gilbert,  a  number  of  small 
depressions  are  formed  in  the  Colorado  region  by 
the  action  of  wind  upon  rocks  devoid  of  vegetation, 
and  Pumpelly  describes  similar  depressions  occurring 
in  the  crystalline  rocks  of  the  region  between  the 
Siberian  frontier  and  the  Great  Wall  of  China,  which 
he  attributes  to  the  removal  of  weathered  rock  by 
wind-action.1 

In  a  humid  climate  it  is  well   known  that  rocks 

are  weathered   unequally  according   to  the  amount 

of  vegetation  which  covers  them.      If  a  fairly  flat 

surface,   diversified    by   small    slopes,   is    formed   of 

1  See  DELABECQUE,  Les  Lacs  Fratifais,  p.  313. 


LAKES  183 

rock  which  is  mostly  bare,  especially  if  the  rock 
contains  much  soluble  material,  as  in  the  case  of 
many  igneous  rocks,  the  lichens,  liverworts,  and 
mosses,  which  retain  the  moisture,  and  hold  it 
against  the  rock,  at  the  same  time  supplying  it 
by  their  decay  with  solvent  organic  acids,  eat  their 
way  into  the  rock,  and  furnish  a  superficial  soil,  in 
which  grass,  heather,  and  other  plants  grow,  and 
allow  the  process  to  continue  on  a  larger  scale. 
If  for  any  reason  the  conditions  should  change 
and  the  vegetation  die,  the  vegetable  matter  and 
decomposed  rock  beneath  may  be  removed  by  the 
wind,  giving  rise  to  a  small  rock  basin.  Little 
basins  of  this  character,  a  few  feet  or  yards  in 
diameter,  are  often  met  with  in  the  English  Lake 
District  in  every  stage  of  formation.  In  some 
cases  we  may  strip  off  the  vegetation,  and  find  the 
depression  beneath,  often  containing  some  incoherent 
weathered  rock  particles ;  at  other  times  most  of 
the  vegetation  has  disappeared,  and  only  a  little 
peaty  material  is  left  at  the  bottom  of  a  pool. 
How  far  this  process  is  responsible  for  the  for- 
mation of  pools  of  any  size  is  unknown,  but  it 
should  be  taken  into  account  when  discussing  the 
origin  of  small  rock  basins. 

The  other  agent  which  has  been  considered 
capable  of  producing  rock  basins,  often  of  consider- 
able size,  is  ice,  and  it  is  necessary  to  refer  to  this 
at  some  length. 

M.  G.  de  Mortillet  in  1859  suggested  that  the 
Alpine  lakes  had  been  filled  up  with  alluvial  deposits 
and  afterwards  excavated  by  glacial  action  ;  and  in 
the  same  year  the  late  Sir  Andrew  Ramsay  put 
forward  his  well-known  theory  that  the  basins  had 


1 84    SCIENTIFIC   STUDY   OF   SCENERY 

been  scooped  out  of  the  solid  rock  by  glacial 
action,  and  afterwards  applied  the  theory  to  account 
for  lakes  in  various  regions,  including  even  the 
great  fresh  -  water  lakes  of  Canada.  Evidence  in 
support  of  this  theory  was  subsequently  advanced 
by  many  writers,  among  whom  special  mention 
may  be  made  of  Mr.  Clifton  Ward,  whose  work  on 
the  lakes  of  English  Lakeland  was  distinguished  by 
the  care  which  marked  all  the  work  of  this  lamented 
geologist,  whose  labours  have  been  fitly  recorded 
by  Canon  Rawnsley  in  his  Literary  Reminiscences 
of  the  Lake  District.  Many  writers  have  attacked 
the  theory  from  various  points  of  view,  and  even 
at  the  present  day  there  is  a  considerable  diversity 
of  opinion  as  to  the  capacity  of  ice  to  excavate 
rock  basins,  some  denying  it  in  toto,  while  others, 
admitting  its  power  to  hollow  out  small  basins,  as 
those  in  which  many  of  our  upland  tarns  lie,  or 
even  the  larger  lakes  of  an  area  like  North  Wales, 
deny  its  power  to  form  basins  like  those  in  which 
the  waters  of  the  greater  Alpine  lakes  are  upheld. 

We  shall  have  occasion  to  speak  about  the  asserted 
erosive  power  of  ice  in  a  chapter  devoted  to  con- 
sideration of  glaciers,  and  in  the  meantime  may 
observe  that  in  order  to  prove  that  ice  can  excavate 
a  basin  we  must  show,  first,  that  the  actual  rock 
basin  exists,  and,  secondly,  that  it  cannot  have  been 
formed  in  any  other  way  than  by  the  erosive  action 
of  ice,  which,  by  the  way,  will  probably  be  found 
to  be  a  matter  of  considerable  difficulty.  Not  only 
must  the  contour  of  the  lake  shores  be  examined, 
but  a  complete  survey  of  the  subaqueous  contours 
is  also  necessary.  In  only  a  few  cases  has  this 
been  done,  notably  by  Mill  and  Delabecque ;  and 


LAKES  185 

we  shall  consider  the  results  of  their  work  and  its 
bearing  upon  the  question  of  glacial  erosion  in  the 
succeeding  chapter.  In  the  meantime  we  may  call 
attention  to  recent  writings  where  the  existence  of 
rock  basins  of  small  size  has  been  asserted,  which 
it  is  difficult  to  account  for  as  being  produced  by 
earth  movement  (though  Mr.  Oldham's  observations 
on  the  rock  basins  produced  by  the  Assam  earth- 
quake of  1897  must  always  be  borne  in  mind).  I 
mention  recent  writings  only,  because  those  who 
have  studied  these  basins  in  recent  years  have  been 
fully  alive  to  the  importance  of  establishing  the 
existence  of  live  rock  all  round  the  basin,  and  not 
merely  where  the  stream  issues  from  the  lake,  an 
occurrence  which  was  wont  to  satisfy  many  of  the 
earlier  writers  upon  the  origin  of  lakes  that  they 
were  dealing  with  live  rock  basins,  though  we  have 
had  occasion  to  notice  that  the  water  often  issues 
over  rock  as  the  result  of  diversion  of  drainage  by 
glacial  or  other  interference,  and  accordingly  the 
dam  of  accumulated  material  may  occur  at  any 
point  around  the  margin  of  the  lake. 

Mr.  H.  P.  Gushing,  in  a  description  of  the  Muir 
glacier  of  Alaska,1  describes  a  number  of  diminutive 
pools  on  the  tops  of  low  hills  near  the  termination 
of  the  glacier,  some  of  the  hills  projecting  from  its 
mass.  The  pools  are  very  shallow,  and  only  a 
few  yards  in  diameter;  and  though  the  shores  of 
some  are  partly  formed  of  glacial  debris,  "  some 
of  them  clearly  occupy  rock  basins,  rock  in  places 
being  readily  traced  all  round  them."  He  states 
that  all  the  basins  which  he  saw  "  lie  in  small 
valleys  on  the  mountain  -  tops,  whose  presence 

1  GUSHING,  H.  P.,  American  Geologist,  189 r. 


1 86     SCIENTIFIC   STUDY   OF   SCENERY 

seemed  to  depend  on  the  fissure  systems  and  on 
the  varying  depths  to  which  loosening  of  blocks 
had  taken  place " ;  and  further,  "  That  the  glacier 
has  done  little  more  than  to  remove  the  loosened 
rock  and  polish  the  resulting  surface  is  shown  in 
a  vast  number  of  localities."  The  ice  in  this  case 
appears  to  have  removed  blocks  which  had  become 
detached  as  the  result  of  weathering. 

A  paper  by  Professor  Bonney1  is  devoted  to  con- 
sideration of  "  Some  Small  Lake  Basins  in  the 
Lepontine  Alps."  '  He  gives  proofs  of  the  existence 
of  four  rock  basins  holding  the  waters  of  the  Lago 
di  Tremorgio,  Lake  Ritom,  Lake  Cadagno,  and  Lake 
Tom,  in  the  Val  Bedretto  and  Val  Piora.  Sir  John 
Lubbock2  remarks  of  two  of  these:  "Some  of  the 
smaller  lakes  in  these  regions,  as,  for  instance,  those 
of  Cadagno  and  Tremorgio,  are  '  meres '  or  lakes  of 
sinking,  like  those  of  Cheshire."  But  Professor 
Bonney,  though  he  speaks  with  extreme  caution 
concerning  their  origin,  seems  to  admit  the  possi- 
bility of  their  formation  by  glacial  erosion.  Of  Lake 
Ritom  he  writes  :  "  This  basin,  then,  the  part  which 
lies  below  the  present  contour  line  of  6000  feet  (in 
round  numbers),  is  the  utmost  that,  in  my  opinion, 
can  possibly  be  attributed  to  the  erosive  action  of 
ice." 

M.  Delabecque,  like  Professor  Bonney,  is  not  a 
believer  in  the  efficacy  of  ice  as  a  former  of  lake 
basins  on  a  large  scale.  In  his  work  on  the  French 
lakes,3  when  giving  a  summary  of  the  various  lakes 

1  BONNEY,  Professor  T.  G.,   Geological  Magazine,  dec.  iv.,  vol.  v. 
(1898),  p.  15. 

2  LUBBOCK,  Sir  J.,  The  Seen  ry  of  Switzerland >  p.  448. 

3  Les  Lacs  FratKais,  p.  343. 


LAKES  187 

of  France  formed  in  different  ways,  he  concludes  with 
a  list  of  lakes  due  to  the  excavation  by  glaciers  of 
the  weathered  parts  of  rocks,  including  all  the  lakes 
which  cannot  be  attributed  to  any  of  the  other  causes 
which  he  has  previously  considered.  The  list  is  as 
follows : — 

"In  the  (French)  Alps:  The  lakes  of  Sept-Laux,  the 
principal  lakes  of  the  massif  of  Belledonne  (except 
Lake  Robert),  Lake  Cornu,  Lac  de  Rabuons,  and 
most  of  the  lakes  situated  in  the  eruptive  rocks  and 
crystalline  schists. 

"  In  the  Jura  :  Lake  de  Paladru  (?). 

"  In  the  Vosges  :  Lake  de  Retournemer. 

"On  the  Central  Plateau:  Lake  de  la  Cre'gut,  de 
Laspialade,  many  of  the  small  lakes  of  the  plateau 
de  1'Artense,  and  of  the  neighbourhood  of  Riom-es- 
Montagne. 

"  In  the  Pyrenees :  Lacs  d'Artouste,  d'Arrius,  de  Migue- 
lou,  de  Gaube,  d'Estom,  d'Espingou,  de  Saousat, 
d'Oo,  the  lakes  of  Port  de  Venasque,  Lac  Bleu 
or  de  Lesponne,  the  lakes  of  the  massif  of 
Neouvieille  and  of  Caillaouas,  Naguille,  Lanoux, 
Garbet,  Lers  (?),  Bassie's,  of  the  waste  of  Carlitte, 
and  generally  the  greater  part  of  the  lakes  situated 
on  eruptive  rocks  and  crystalline  schists." 

He  concludes,  "  I  need  scarcely  say  in  conclusion  that 
this  list  is  far  from  being  definite,  and  that  the  future 
progress  of  geology  will  certainly  modify  it." 


CHAPTER   XII. 

LAKES  (Continued) 

HITHERTO,  while  speaking  of  the  origin  of 
lakes,  we  have  said  little  of  the  nature  of  the 
outlines  of  lake  shores,  or  of  the  topography  of  their 
basins,  and  we  may  now  proceed  to  consider  the 
character  of  the  shores  and  basins  during  different 
periods  of  the  existence  of  lakes. 

Topographical  Features  of  the  Shores  and  Basins 
of  Lakes.— The  features  of  a  lake  depend,  in  the 
first  place,  upon  its  origin,  and,  secondly,  upon  the 
changes  which  have  taken  place  after  its  formation, 
some  parts  undergoing  erosion,  while  others  receive 
deposit.  The  diversity  in  the  structures  of  lakes, 
due  to  difference  of  origin,  has  already  been  alluded 
to  in  passing.  A  crater  lake  often  presents  a  circular 
outline,  and  may  be  very  deep  as  compared  with 
its  horizontal  extent ;  a  lake  of  subsidence,  due  to 
underground  solution,  may  vary  extensively  both  as 
regards  outline  and  nature  of  the  hollow ;  one  formed 
by  erosion  of  a  rock  basin  would  present  a  general 
basin-shaped  cross-section  ;  lastly,  lakes  formed  by 
blocking  of  pre-existing  valleys,  whether  by  forma- 
tion of  dams  of  accumulation,  or  by  differential  uplift 
in  a  direction  transverse  to  the  valley  (or,  what 
comes  to  the  same  thing,  sinking  of  the  upper 
portion  of  the  valley  in  a  downward  direction),  will 


LAKES  189 

be  distinguished  by  possessing  a  continuation  of  the 
subaerial  features  of  the  valley  sides  beneath  the 
margin  of  the  lake.  These  lakes  are  indeed  drowned 
portions  of  river  valleys,  and  will  at  first  possess  the 
physiographical  features  of  such  valleys,  which  may 
be  afterwards  modified  by  erosion,  and  especially  by 
accumulation.  We  may  consider,  in  the  first  place, 
the  subaqueous  features  of  lakes  of  the  last  class,  and 
then  refer  to  their  marginal  topography.  The  original 
subaqueous  features  will  naturally  become  masked  in 
lakes  which  have  received  a  supply  of  sediment  for 
any  length  of  time,  and  accordingly  we  cannot  ex- 
pect to  find  signs  of  features  which  were  produced 
by  subaerial  denudation  before  the  formation  of  the 
barrier  in  all  lakes  which  form  drowned  parts  of 
former  river  valleys ;  but  we  have  several  cases  in 
which  these  features  are  developed  to  a  sufficient 
extent  to  show  that  we  are  not  dealing  with  ex- 
amples of  basins  hollowed  out  by  erosion.  Dr.  Mill's 
work  on  the  English  Lake  District  brought  to  light 
examples  of  submerged  river  valleys  beneath  the 
waters  of  some  of  the  lakes.  In  Windermere  "  a 
channel  about  100  yards  wide  .  .  .,  commencing 
off  Ferry  Head,  runs  close  to  the  west  shore, 
and  spreads  out  to  nearly  the  full  width  of  the 
lake  at  Storr's  Point.  This  channel  suggests  the 
remnant  of  an  old  river  valley  by  its  narrow  and 
sinuous  course."  It  has  no  doubt  been  modified  by 
subsequent  accumulation  of  deposit.  In  the  same 
lake,  a  valley  which  enters  near  the  head,  in  a  direc- 
tion at  right  angles  to  the  long  axis  of  the  lake,  is 
continued  beneath  the  water  in  Pull  Bay;  and  the 
Troutbeck  valley,  on  the  east  side,  is  also  found  to 
run  below  the  lake,  though  here  the  contour  lines 


190     SCIENTIFIC   STUDY   OF   SCENERY 

are  modified  as  the  result  of  subsequent  deposition. 
Again,  in  Ullswater  the  Fusedale  valley  is  submerged 
where  it  joins  the  lake,  as  indicated  by  the  course  of 
the  sublacustrine  contour  lines  around  the  bay  at 
Howtown.  In  Ullswater  and  Crummock  are  excellent 
examples  of  subaqueous  cliffs.  Two  soundings  taken 
near  the  head  of  the  former  lake,  at  a  distance  of  six 
feet  from  the  shore,  gave  in  one  case  a  depth  of 
forty-four,  in  the  other  a  depth  of  forty-eight,  feet ; 
and  in  Crummock,  "  at  Hause  Point,  on  the  right,  the 
cliff  ran  sheer  down,  seventy  feet  being  found  eight 
feet  off  the  rock."  The  floors  of  Buttermere,  Crum- 
mock, and  Wastwater  are  exceedingly  flat  for  long 
distances,  and  suggest  the  existence  of  submerged 
alluvial  flats  formed  before  the  conversion  of  valleys 
into  lakes.  Again,  the  existence  of  the  ice-smoothed 
rock  surfaces  with  a  rough  face  on  the  lee  sides,  both 
above  and  below  water,  on  rocky  islets,  as  seen  in 
Windermere  and  Ullswater,  gives  another  example 
of  the  identity  of  subaerial  and  sublacustrine  scenery 
in  the  case  of  the  lakes  of  Lakeland.  This  identity 
of  the  scenery  above  and  below  water  is  strong  evi- 
dence that  the  lakes  of  Lakeland  are  merely  drowned 
lower  portions  of  river  valleys. 

More  striking  subaqueous  features  are  found  in  the 
Canadian  lakes.  Many  of  these  have  been  recorded 
by  Dr.  J.  W.  Spencer,1  and  some  examples  may 
be  quoted  from  his  works.  In  Lake  Ontario  he 
has  "  shown  that  a  narrow  buried  channel,  of 
ninety  fathoms  depth  or  more,  extends  for  about 

1  See  especially  SPENCER,  J.  W.,  "A  Short  Study  of  the  Features 
of  the  Lower  Great  Lakes  during  the  Great  River  Age,"  Proc.  Amer. 
Assoc.  for  Advancement  of  Science,  vol.  xxx.  ;  also  the  same  author, 
Quart.  Jour.  Geol.  Soc.,  vol.  xlvi. 


LAKES  191 

ninety  miles  from  near  Oswego  to  the  seventy- 
eighth  meridian,  and  at  a  somewhat  less  depth 
(seventy  fathoms)  to  near  the  meridian  of  the 
Niagara  river.  .  .  .  From  the  Canadian  shore  the 
lake  bottom  slopes  gently,  .  .  .  but  from  the  New 
York  side  the  slope  for  three  or  four  miles  is 
double  that  on  the  northern  side,  and  then  comes 
a  plunge  over  the  face  of  an  escarpment.  This 
escarpment  is  quite  comparable  with  a  subaerial 
escarpment,  as  that  of  the  Niagara  river.  The 
escarpment  can  be  traced  for  nearly  100  miles." 
Spencer  has  shown  that  Lakes  Huron  and  Michi- 
gan also  possess  the  characters  of  drowned  subaerial 
valleys  traversed  by  river  systems.  Huron  possesses 
a  submerged  escarpment,  300  to  450  feet  high,  facing 
the  north-east.  Michigan  "  is  in  part  bounded  by 
vertical  submerged  escarpments,  one  of  which,  upon 
the  eastern  side,  has  a  height  of  500  feet." 

Submerged  valleys  occur  in  Switzerland,  at  the 
heads  of  Geneva  and  Constance,  but  Forel  has  shown 
that  these  are  due  to  deposition,  and  not  to  the 
existence  of  drowned  river  valleys  of  erosion  ;  the 
denser  water  of  the  river,  charged  with  very  fine 
alluvial  material,  is  bounded  by  walls  of  lighter  water, 
and  where  it  meets  with  these,  deposits  its  alluvium 
in  embankments  which  direct  the  course  of  the  sub- 
lacustrine  stream.1 

The  shore  lines  of  lakes  will  at  the  outset  be 
determined  by  the  existing  nature  of  the  ground 
at  the  time  of  formation  of  the  lake,  in  those  lakes 
which  are  due  to  the  drowning  of  a  subaerial  surface 

1  FOREL,  F.  A.,  Le  Levian,  vol.  i.,  p.  385  ;  and  DELABECQUE,  A., 
Archives  des  Sciences  Physiques  et  Naturelles,  4eme  Periode,  vol.  i., 
Geneva. 


192     SCIENTIFIC   STUDY   OF   SCENERY 

by  formation  of  barriers.  Accordingly  the  relation- 
ship between  depth  and  superficial  extent  will  depend 
upon  the  relation  between  width  and  depth  of  the 
inequalities  in  which  lakes  are  formed.  Plateau  lakes 
on  the  whole  will  be  comparatively  shallow,  valley 
lakes  comparatively  deep.  Moreover,  the  width  of 
the  lake,  as  compared  with  its  depth,  will,  in  the  case 
of  valley  lakes,  depend  upon  the  character  of  the 
valley.  Wide  shallow  valleys  will  produce  wide 
shallow  lakes ;  deep  narrow  valleys  will  give  rise  to 
deep  and  narrow  sheets  of  water.  Thus  in  the  Lake 
District  the  comparatively  narrow  valleys  above 
Ullswater  and  Windermere  continue  as  deep  and 
narrow  river-like  lakes,  while  the  wide  shallow  lower 
part  of  Borrowdale  is  continued  in  the  lakes  of 
Derwentwater  and  Bassenthwaite,  which  present  the 
same  characteristics. 

If  the  original  valley  was  tortuous,  the  lake  will 
be  tortuous,  like  our  own  Ullswater,  and  the  lakes  of 
Lucerne,  Como,  and  Maggiore. 

Again,  where  tributaries  have  cut  their  valleys 
down  to  the  level  of  the  main  valley,  lakes  formed 
by  barriers  will  extend  up  the  tributary  valleys  as 
bays,  the  bay  running  up  the  tributary  to  a  greater 
or  less  extent  according  to  the  slope  of  the  Thalweg. 
If  the  slope  is  steep,  the  bay  will  be  relatively  small ; 
if  gentle,  the  bay  will  form  a  deep  indentation.  Bays 
of  this  character  naturally  become  filled  by  sediment, 
as  we  shall  see  presently,  when  the  lake  has  existed 
for  some  time,  but  if  the  supply  of  sediment  be 
small,  and  the  bay  large,  the  bay  may  remain  for  a 
considerable  period.  The  plateau  tarns  of  Lakeland 
and  North  Wales  are  frequently  indented  with  small 
bays,  corresponding  with  minor  valleys.  Among 


LAKES  193 

the  larger  lakes,  we  have  already  noticed  the  bays 
extending  up  the  Pullwyke  and  Troutbeck  valleys 
in  Windermere,  and  the  Fusedale  valley  at  How- 
town  in  Ullswater.  In  the  Alpine  region  we  may 
notice  the  two  arms  of  Lucerne  occupying  tributary 
valleys,  and  the  arm  of  Maggiore  extending  up  the 
Val  d'Ossola. 

The  outlines  of  lakes  forming  drowned  portions 
of  river  valleys  will  at  the  outset  be  marked  by 
considerable  irregularity,  abrupt  angles  being  fre- 
quently observable  where  the  original  ground  was 
uneven.  This  may  be  seen  at  the  present  day  with 
the  artificially  raised  Thirlmere,  a  useful  object-lesson 
furnished  by  the  Manchester  Corporation  to  show  the 
difference  between  a  newly  formed  lake  and  one  that 
has  adjusted  itself  to  a  stable  condition.  These 
outlines  will  be  subsequently  modified  as  results  of 
erosion  and  deposition. 

Erosion  does  not  exert  any  profound  effect  upon 
the  shores  of  small  lakes,  though  considerable  erosive 
action  occurs  on  larger  ones,  causing  gradual  reces- 
sion, especially  of  the  more  salient  points  of  a  lake 
shore,  with  formation  of  cliffs.  This  is  seen  in  the 
large  Canadian  lakes,  and  also  those  of  Sweden,  which 
are  often  stirred  by  storms  of  considerable  violence. 
Mill  gives  a  figure  in  his  work  on  the  English  lakes 
showing  effect  of  wave  erosion  on  the  incoherent 
material  of  the  Troutbeck  delta  at  Windermere. 
Small  cliffs,  simulating  sea-cliffs,  may  be  produced 
by  erosion,  and  a  consideration  of  the  formation  of 
cliffs  may  be  deferred  until  we  consider  the  action 
of  the  sea. 

The  most  marked  changes  are  produced  by  accu- 
mulation, which  modifies  to  a  very  great  extent  the 
o 


194    SCIENTIFIC   STUDY   OF   SCENERY 

original  outlines  of  a  lake.  Thus  Mill  has  contrasted 
the  straight  line  of  the  south-east  side  of  Hawes- 
water,  which  is  practically  its  primitive  outline,  with 
the  extremely  sinuous  north  -  western  margin,  pro- 
duced by  subsequent  accumulation  of  deposit. 

The  first  accumulation  to  be  considered  is  the 
beach  which  surrounds  a  sheet  of  water.  Now  lake- 
beaches  merely  differ  from  sea  -  beaches  in  the 
absence  of  tidal  action,  and  their  essential  features 
are  the  same,  and  their  structure  and  origin  will 
be  more  fully  considered  hereafter.  It  is  sufficient 
here  to  notice  that  beaches  are  formed  by  on-shore 
travel  of  loose  material,  tending  to  fill  up  the  hollows 
between  salient  points  by  deposition  of  material, 
which  assumes  a  concave  curve  characteristic  of 
lakes  which  have  adjusted  themselves  to  conditions 
of  stability.  The  curvature  of  bays  is  one  of  the 
most  striking  features  in  the  scenery  of  a  lake,  and 
the  angular  outlines  of  a  recently  dammed  lake  like 
Thirlmere  or  the  sheet  of  water  at  Tarn  Howes, 
near  Coniston,  form  a  marked  contrast  to  the  flow- 
ing curves  of  a  lake  whose  original  angularities 
have  been  replaced  by  the  concavities  due  to  beach 
formation.  The  view  of  Haweswater  in  the  accom- 
panying plate  shows  the  curved  bays  of  the  north- 
western shore  on  the  right,  and  the  straight  line  of 
the  south-eastern  shore  on  the  left,  of  the  figure. 

Next  we  have  the  delta,  formed  where  a  stream 
enters  the  lake.  The  velocity  of  the  water  is  at  once 
checked  on  entering,  and  it  deposits  its  material, 
gradually  converting  a  portion  of  the  lake  into  a 
flat  tract  of  land,  which  ordinarily  forms  a  fan,  with 
semicircular  margin,  though  this  margin  may  be 
greatly  complicated  in  many  ways,  especially  by 


LAKES  195 

the  tendency  of  streams  to  deposit  ridges  on  their 
sides  and  build  out  parallel  embankments  rising 
above  the  surface  for  some  distance  beyond  the 
general  margin  of  the  delta.  Moreover,  the  shallow 
waters  in  front  of  the  deltas  are  frequently  occupied 
by  a  growth  of  marsh  and  water  plants,  as  reeds  and 
water-lilies,  which  form  a  peaty  surface  sometimes 
sufficiently  firm  to  give  rise  to  land,  beyond  the 
general  margin  of  the  delta  which  is  due  to  mecha- 
nical deposit  of  sediment,  as  seen  at  the  head  of 
Derwentwater.  The  plate  with  the  figure  of  Sty 
Head  Tarn,  besides  exhibiting  a  delta  at  the  foot 
of  the  lake  which  originated  the  tarn,  shows  two 
others ;  that  at  the  head,  seen  in  the  foreground, 
which  has  considerably  diminished  the  size  of  the 
lake,  and  another  on  the  left-hand  side,  with  a  minor 
delta  growing  out  from  it,  forming  a  promontory. 

When  a  very  important  river  enters  a  lake  between 
head  and  foot,  it  will  build  out  its  delta  until  the  lake 
is  converted  into  two  sheets  of  water,  connected  by 
a  narrow  strait  on  the  side  opposite  to  that  on  which 
the  delta  is  growing.  Haweswater  is  thus  converted 
into  two  sheets,  known  as  High  Water  and  Low 
Water,  by  the  straits  at  Measand,  where  the  lake  is 
narrowed  from  a  width  of  half  a  mile  to  about  100 
yards.  In  the  figure  of  Haweswater  the  Measand 
delta  is  seen  as  a  dark  straight  line  just  above  and  to 
the  west  of  the  boat-house,  and  concealing  High 
Water  beyond  it,  the  straits  being  visible  between  the 
delta  and  the  dark  slope  on  the  left.  As  the  outward 
growth  of  deltas  of  this  nature  proceeds,  they  may, 
and  often  do,  eventually  form  completely  across  the 
lake,  severing  it  into  two,  as  in  the  case  of  Butter- 
mere  and  Crummock,  and  Bassenthwaite  and  Derwent- 


196     SCIENTIFIC   STUDY   OF   SCENERY 

water  in  the  Lake  District,  the  two  lakes  of  Llanberis 
in  Wales,  and  Brienz  and  Thun  in.  Switzerland,  to 
mention  a  few  examples.  When  this  happens  the 
two  lakes  are  separated  by  a  flat  alluvial  tract,  which 
may  be  completely  submerged  after  heavy  rains,  when 
the  lake  level  rises,  an  event  which  occurs  not  in- 
frequently in  the  case  of  Derwentwater  and  Bassen- 
thwaite. 

Screes  and  dry  deltas  often  encroach  upon  lakes, 
altering  the  original  topography  of  their  shores. 
The  dimensions  of  many  of  our  upland  tarns  have 
considerably  diminished  as  the  result  of  material 
slipping  down  the  slopes  or  falling  down  scree-shoots 
into  the  water.  The  well-known  screes  of  Wastwater, 
illustrated  in  the  plate,  have  produced  considerable 
diminution  of  the  area  of  the  lake,  and  also  pro- 
foundly affected  the  scenery  of  its  shores. 

Lastly,  we  have  avalanches  of  rock  descending 
from  the  hill-sides  in  mountain  regions  and  tending 
to  diminish  the  area  of  the  lake  when  they  fall  into 
the  water  surrounding  the  shore.  A  somewhat 
peculiar  result  of  the  fall  of  avalanches  is  described 
in  Delabecque's  monograph  on  the  French  lakes, 
the  explanation  of  the  phenomenon  having  been 
given  by  MM.  J.  Vallot  and  E.  Belloc.  In  certain 
regions,  as  the  Pyrenees,  avalanches  fall  in  winter 
and  the  early  spring,  and  are  arrested  on  the  frozen 
surface  of  the  lake.  When  it  thaws  the  materials 
fall  to  the  floor  of  the  lake,  and  become  rearranged 
to  some  extent,  giving  rise  to  a  mound,  which  some- 
times forms  an  island  and  sometimes  a  little  second- 
ary basin  between  the  avalanche  and  the  lake.1 

By  these  various  processes — deposition  of  sediment 
1  See  DELABECQUE,  Les  Lacs  Franfais,  p.  364. 


t. 


I 


LAKES  197 

in  deltas,  formation  of  screes  and  avalanches,  and 
general  growth  of  vegetation  in  the  shallows  pro- 
duced by  growth  of  alluvium— lakes  are  gradually 
rilled  up.  At  the  same  time  the  top  of  the  lake 
at  the  exit  may  become  lowered  by  erosion,  though, 
as  before  stated,  the  erosion  is  slight,  owing  to  the 
general  absence  of  sediment.  Accordingly  we  find 
all  stages  from  the  existence  of  lakes  in  which  the 
diminution  of  area  has  commenced,  through  those 
in  which  the  tract  of  water  consists  of  a  pool 
surrounded  by  peat  moss,  to  the  final  extinction 
of  the  lake  and  its  replacement  by  turbary,  or  peat 
moss  produced  by  growth  of  marsh  vegetation  on  the 
flat  alluvial  tract  caused  by  the  silting  up  of  the 
lake.  These  peat  mosses  are  usually  very  abundant 
in  mountain  regions,  and  testify  to  the  large  number 
of  lakes  which  once  existed,  and  have  now  been 
destroyed  by  silting. 

Islands  in  Lakes.  —  It  is  very  doubtful  how  far 
islands  can  exist  in  lakes  produced  by  erosion, 
though,  assuming  that  erosion  can  produce  lakes,  the 
existence  of  isolated  masses  of  hard  rock  among 
softer  rocks  might  permit  the  formation  of  islands. 
In  lakes  produced  by  "drowning"  of  the  bottoms  of 
river  valleys,  any  isolated  hill  standing  above  the 
general  level  of  the  valley  would  remain  as  an  island. 
The  rocky  islands  of  Ullswater  and  Windermere 
seem  to  be  of  this  nature ;  and,  as  pointed  out  by 
Mill,  submergence  of  the  Ullswater  valley  to  the 
extent  of  another  hundred  feet  would  convert  Hallin 
Fell  into  an  island  a  mile  in  diameter.  Other  islands 
are  produced  by  existence  of  incoherent  material  in 
ridges ;  thus,  as  suggested  by  Mill,  the  islands  of 
Derwentwater,  composed  of  masses  of  gravel,  sand, 


198     SCIENTIFIC   STUDY  OF  SCENERY 

and  clay,  are  probably  ridges  of  glacial  drift  which 
stood  out  above  the  general  level  of  the  floor  of  the 
valley  to  a  sufficient  height  to  escape  submergence. 
The  formation  of  islands  by  avalanches  subsequently 
to  the  time  when  the  lake  came  into  being  has  been 
described  above. 

The  so-called  floating  islands,  which  are  sometimes 
found,  may  be  referred  to,  though  they  are  of  little 
interest  to  the  student  of  scenery.  One  occasionally 
appears  in  Derwentwater,  and  the  little  lake  Llyn-y- 
dywarchen,  between  Carnarvon  and  Beddgelert,  in 
North  Wales,  receives  its  name  from  a  similar  appear- 
ance. It  would  seem  that  these  floating  islands  are 
simply  masses  of  peaty  vegetable  matter  on  the 
floors  of  shallow  parts  of  the  lake,  which,  owing  to 
accumulation  of  light  gases,  formed  by  decomposi- 
tion of  vegetable  matter,  are  occasionally  buoyed  up 
to  such  an  extent  that  they  float  upon  the  surface, 
until  the  gases  are  disengaged  sufficiently  to  allow 
them  to  sink  once  more  to  the  bottom.  This  is  the 
explanation  given  by  Jonathan  Otley,  the  old  Lake 
District  guide  (whose  geological  work  has  hardly 
received  the  recognition  which  it  merits),  in  a  paper 
published  in  the  Lonsdale  Magazine  in  1820  (p.  15), 
and  there  is  very  little  doubt  that  it  is  substantially 
correct 

Colour  of  Lakes. — The  charm  of  lake  scenery  de- 
pends to  a  large  extent  on  the  limpidity  of  the  water 
and  the  varying  play  of  colours  upon  the  surface. 
The  transparency  of  the  water  is  due  to  the  deposi- 
tion of  sediment  where  the  streams  enter  the  lake, 
leaving  the  main  mass  of  the  waters  free  from 
sediment,  except  when  violent  floods  bring  very  fine 
particles  into  a  lake  of  no  great  superficial  extent 


LAKES  199 

The  question  of  colour  is  more  complex,  and  merits 
some  consideration,  especially  as  much  diversity  of 
opinion  has  arisen  concerning  the  cause  of  colour  in 
certain  lakes.  Over  and  above  the  ever-varying  play 
of  colour  due  to  changes  in  the  sky,  we  find  that 
certain  lake  waters  possess  a  very  definite  hue ;  the 
intense  blue  of  Geneva,  for  instance,  is  known  to 
everyone. 

The  water  of  lakes  may  be  blue,  green,  yellow,  or 
absolutely  colourless.  M.  Forel  has  constructed  a 
scale  of  colours  for  reference,  made  by  mixing  to- 
gether ammoniated  sulphate  of  copper  and  chromate 
of  potassium.  The  scale  extends  from  I.  to  XL,  I. 
containing  none  of  the  chromate  solution,  while  XL 
contains  65  per  cent  of  the  chromate  and  only  35 
of  the  copper  sulphate.  The  colours  from  I.  to  IV. 
of  the  scale  are  blue,  those  between  V.  and  VIII. 
green,  and  IX.  to  XL  yellow. 

Of  blue  lakes,  we  find  in  our  own  country  two 
tarns  on  Snowdon — namely,  Llyn  -  dur  -  Arddu  and 
Glaslyn — of  an  intense  indigo  colour ;  and  the  larger 
Llyn  Llydaw  has  much  the  same  hue.  In  Switzer- 
land, Geneva  has  already  been  referred  to.  There 
are  also  several  small  lakes,  as  the  Blaue  Seeli,  near 
Kandersteg,  and  the  Lac  Bleu  de  Lucel,  near  Arolla. 
The  cause  of  this  colour  has  been  a  subject  for  much 
discussion.  Sir  H.  Davy  suggested  that  the  waters 
of  Geneva  owed  their  colour  to  the  presence  of 
iodine ;  and  other  writers  have  supposed  that  it  was 
due  to  minute  particles  of  glacier  mud. 

It  is  now  known  that  the  true  colour  for  distilled 
water  is  blue.  If  distilled  water  be  placed  in  a  long 
tube,  and  viewed  through  the  length  of  the  tube,  it 
will  appear  blue.  Accordingly  it  is  found  that  the 


200     SCIENTIFIC   STUDY   OF   SCENERY 

water  of  the  lakes  just  referred  to  is  extremely  pure, 
being  free  from  any  appreciable  amount  of  organic 
matter,  and  also  devoid  of  sediments. 

In  the  Gazette  de  Lausanne  for  October,  1887, 
Professor  Forel  describes  the  waters  of  the  Lac 
Bleu  de  Lucel,  a  lake  about  200  feet  long  and 
thirteen  feet  deep,  fed  by  a  spring  which  rises  from 
the  ground  just  above  the  lake.  He  finds  that  the 
waters  of  this  lake  are,  so  far  as  is  known,  the  most 
transparent  of  all  sheets  of  water,  and  they  are  devoid 
of  life.  I  had  the  opportunity  of  seeing  the  lake  in 
sunshine,  and  also  when  the  sky  was  completely 
overcast,  and  under  the  latter  conditions  the  colour 
was  exquisite. 

The  green  colour  may  be  due  to  reflection  of  light 
from  a  sandy  bottom  through  shallow  water.  Again, 
solution  of  organic  substances,  such  as  humic  and 
ulmic  acids  derived  from  vegetable  matter,  may,  as 
shown  by  Forel,  convert  blue  water  into  green,  or 
even  into  yellow  or  brown,  when  the  water  is  sur- 
rounded by  peat  mosses.  This  accounts  for  the 
green  colour  of  many  of  the  upland  tarns  of  our  hill 
regions,  which  frequently  occur  in  association  with 
peat  mosses  due  to  their  partial  silting  up.  Again, 
a  green  or  yellow  colour  may  be  produced  by 
abundance  of  coloured  microscopic  organisms  in  the 
water,  as  suggested  by  Delabecque  in  the  Lac  de 
la  Laudie,  on  the  central  plateau  of  France,  which 
has  a  colour  corresponding  with  No.  XL  in  Forel's 
scale. 

Professor  Spring  has  shown  that  blue  distilled 
water  rapidly  loses  its  colour  and  becomes  green,  but 
that  the  addition  of  a  small  proportion  of  bichloride 
of  mercury,  which  will  destroy  organisms,  is  sufficient 


LAKES  201 

to  preserve  the  blue  colour  indefinitely.  Again,  water 
which  does  not  contain  organic  impurities,  but  which 
contains  minute  particles  of  colourless  mud,  as  glacier 
mud  in  suspension,  gives  a  yellow  tint  to  the  water, 
which,  combined  with  its  natural  blue,  produces  a 
green  tint.  To  this  cause  he  attributes  the  green 
colour  of  Neuchatel  and  Constance.  If  the  glacier 
mud  is  very  thick,  the  water  will  be  rendered  turbid 
and  grey,  as  seen  where  glacier  streams  pour  into 
a  lake,  or  where,  unfortunately,  finely  divided  mud 
is  produced  by  mining  operations,  causing  the  grey- 
ness  which  sullies  the  head  of  Ullswater.  Lastly, 
it  has  been  observed  that  some  lakes,  which  are 
ordinarily  green,  occasionally  become  colourless,  and 
Professor  Spring  has  shown  that  this  change  is  pro- 
duced by  the  introduction  of  a  fine  reddish  mud, 
coloured  by  oxide  of  iron,  which  neutralises  the 
green  hue,  and  renders  the  lake  for  the  time  being 
perfectly  colourless. 

On  March  3Oth,  1894,  about  11.30  a.m.,  I  noticed 
an  interesting  phenomenon  on  Windermere  when 
looking  up  the  lake  from  among  the  islands  of 
Bowness  Bay.  The  day  was  perfectly  calm,  and 
the  fells  at  the  head  of  the  lake  were  seen  dimly 
through  a  pearly  blue  haze.  The  sun  was  shining 
brightly  on  the  islands  in  the  foreground,  with  their 
graceful  groups  of  birch,  and  on  the  light  green 
larches  mixed  with  the  darker  firs  on  Furness  Fells. 
From  the  banks  of  the  lake  on  either  side  a  bar 
of  prismatic  colours,  glowing  most  vividly,  stretched 
out  towards  the  centre,  the  red  being  next  the 
shore,  and  the  violet  towards  the  middle  of  the 
lake.  Looking  about  for  an  explanation,  I  found 
that  the  water  around  the  boat  was  glistening  from 


202     SCIENTIFIC   STUDY   OF   SCENERY 

myriad  points,  and  noticed  that  countless  organisms, 
probably  unicellular  algae,  were  floating  in  the  surface 
waters.  Each  of  these  acted  as  a  little  prism,  and 
produced  the  iris  bars  which  gave  so  strangely 
beautiful  an  effect  to  the  whole  scene. 

Effects  due  to  mirage  are  often  seen  on  lakes, 
but  it  is  beyond  our  purpose  to  describe  them  in 
full.  The  fata  morgana  is  often  visible  on  Geneva, 
especially  in  the  spring-time.  A  full  account  of  the 
phenomenon  will  be  found  in  Professor  Forel's  work 
Le  Leman  (vol.  ii.,  pp.  514  et  seg.}. 


CHAPTER  XIII. 
VOLCANOES 

VOLCANIC  hills  and  plateaux  are  produced  by 
accumulation  of  material  which  has  been 
brought  from  the  earth's  interior  in  a  liquid  or 
fragmental  condition  upon  the  pre-existing  surface 
of  the  earth.  It  was  formerly  supposed  that  volcanic 
hills  were  due  to  uplift  of  a  blister-like  mass  of  the 
earth's  crust,  like  the  viscid  bubbles  which  form 
upon  the  surface  of  a  plate  of  hot  porridge  ;  but 
study  of  volcanoes  in  all  states  of  dissection  has 
abundantly  proved  that  the  hills  are  formed  by 
accumulation,  and  the  old  "  elevation-crater  theory " 
has  been  abandoned. 

To  account  for  the  extrusion  of  material  in  a 
molten  state  on  the  earth's  surface,  we  must  take 
three  things  into  consideration,  namely,  the  pro- 
duction of  the  molten  material,  the  formation  of 
lines  or  spots  of  weakness  through  which  it  is 
extruded,  and  the  force  which  brings  the  molten 
matter  to  the  surface;  these  we  may  refer  to  in 
the  above  order. 

If  the  earth  has,  as  generally  supposed,  con- 
solidated from  a  once  fluid  condition,  it  is  possible 
that  some  of  the  originally  molten  material  has 
remained  unconsolidated ;  but  there  is  much  evi- 
dence that  the  greater  part  at  any  rate  of  the  rocks 
203 


204     SCIENTIFIC   STUDY   OF   SCENERY 

which  are  poured  out  on  to  the  earth's  surface  in 
a  molten  condition  have  been  solid,  and  have 
become  liquefied.  Liquefaction  may  be  brought 
about  in  a  solid  rock  by  increase  of  temperature, 
diminution  of  pressure,  or  alteration  of  the  com- 
position of  the  rock,  thereby  lowering  its  melting 
point.  At  the  surface  of  the  earth  the  rocks  are 
solid  owing  to  the  low  temperature  which  prevails 
there.  Observations  have  shown  that  the  tem- 
perature increases  towards  the  interior,  but  so  also 
does  the  pressure,  which  tends  to  neutralise  the 
effects  of  heat,  and  to  keep  rocks  solid  which, 
under  the  ordinary  atmospheric  pressure,  would 
be  fused.  At  a  certain  depth  masses  of  rock  may 
occur  at  a  high  temperature  which  are  solid,  but 
so  near  to  the  fusing  point  that  minor  changes  may 
cause  their  liquefaction,  and  we  may  refer  to  the 
principal  changes  which  have  been  claimed  as 
capable  of  producing  liquefaction.  In  the  first  place, 
transference  of  heat  from  one  rock  to  another  may 
produce  liquefaction  of  a  rock  which  was  previously 
below  its  fusing  point.  Such  transference  must  take 
place,  but  it  is  doubtful  whether  it  can  ever  be  a 
very  potent  factor  in  producing  liquefaction. 

Sir  Humphry  Davy  long  ago  suggested  that  a 
rise  in  temperature  might  occur  as  the  result  of  the 
heat  generated  by  oxidation  of  masses  of  metals 
of  the  alkalies  enclosed  among  the  rocks  of  the 
interior ;  he  was  afterwards  led  to  abandon  the 
suggestion,  but  some  recent  writers  have  maintained 
that  oxidation  of  metals  existing  in  the  elementary 
condition  may  cause  evolution  of  sufficient  heat  to 
produce  liquefaction.  Mr.  Scrope  called  attention 
to  the  effects  which  would  be  produced  by  formation 


VOLCANOES  205 

of  thick  masses  of  sediment  It  is  supposed  that 
surfaces  of  equal  temperature  (isogeotherms)  occur 
approximately  parallel  to  the  surface  of  the  earth. 
An  accumulation  of  some  thousands  of  feet  of 
sediment  would  raise  the  isogeotherms  correspond- 
ingly, and  in  this  way  the  temperature  of  rocks 
previously  in  a  solid  state  might  be  raised  to  their 
fusing  points.  Mr.  R.  Mallet  supposed  that  after 
the  crust  of  the  earth  became  too  rigid  to  adapt 
itself  to  contraction  by  folding  it  would  do  so  by 
crushing,  and  that  belts  of  crushed  rock  would  be 
formed,  and  that  the  friction  due  to  the  crushing 
would  generate  heat  sufficient  to  cause  liquefaction. 

Diminution  of  pressure  might  be  produced  by 
denudation  of  great  masses  of  overlying  sediment 
or  by  uplift  of  portions  of  the  crust  in  domes  and 
arches,  relieving  the  pressure  beneath  the  centres 
of  the  uplifts,  or  by  actual  fissuring  of  the  earth's 
crust.  It  must  be  noted  that,  though  denudation 
would  remove  the  pressure,  it  would  lower  the 
isogeotherms,  and  similarly  accumulation  of  sedi- 
ment, while  raising  the  isogeotherms,  would  increase 
the  pressure. 

Alteration  of  composition,  causing  lowering  of  the 
fusing  point,  was  first  suggested  by  Professor  Guthrie 
as  a  means  of  producing  fusion,  and  has  been  strongly 
advocated  by  Professor  Judd,  especially  to  account 
for  certain  phenomena  connected  with  the  great 
eruption  of  Krakatoa  in  1883.  Guthrie  observed 
that  certain  salts  were  capable  of  forming  unstable 
compounds  with  water,  which  he  termed  cryohy- 
drates,  and  he  suggested  that  analogous  compounds 
might  be  formed  out  of  some  of  the  constituents 
of  rocks.  These  cryohydrates  have  a  lower  melting 


206     SCIENTIFIC   STUDY   OF   SCENERY 

point  than  the  corresponding  anhydrous  com- 
pounds. 

The  capacity  of  these  various  processes  to  produce 
the  requisite  fusion  has  been  very  fully  discussed 
in  many  works  and  memoirs.  It  is,  of  course, 
impossible  to  enter  here  into  the  technicalities 
requisite  for  the  comprehension  of  the  various 
arguments,  but  enough  has  been  said  to  show  that 
liquefaction  may  be  produced  in  more  than  one 
way,  and  the  probability  is  that  the  complexities 
of  volcanic  phenomena  can  only  be  accounted  for 
on  the  supposition  that  the  causes  which  produce 
liquefaction  are  also  complex. 

The  production  of  planes  or  lines  of  weakness, 
along  which  material  may  be  extruded  upon  the 
earth's  surface,  has  been  already  referred  to  when 
discussing  the  changes  produced  by  movements  of 
the  earth's  crust;  it  was  then  seen  that  fracture  as 
well  as  folding  frequently  resulted  from  movements 
of  the  superficial  covering  of  the  earth.  It  now 
remains  for  us  to  call  attention  to  the  distribution 
of  the  planes  of  disruption,  and  to  trace  their 
connection  with  the  distribution  of  volcanic  vents. 
It  has  long  been' known  that  volcanoes  are  usually 
developed  along  definite  lines,  specially  well  seen 
in  the  case  of  the  volcanoes  which  border  the 
western  coast  line  of  the  New  World,  but  also 
easily  traceable  in  other  areas  of  vulcanicity.  Now 
the  most  important  of  these  lines  occur  along  the 
septa  of  the  great  earth -waves,  which  are  broken 
across  by  gigantic  fault-planes,  and  it  is  here  that 
volcanic  activity  is  most  rife.  The  reader  will  find 
this  connection  between  the  distribution  of  volcanoes 
and  that  of  the  great  wave  septa  discussed  in 


VOLCANOES  207 

Professor  Lapworth's  presidential  address  to  Section  C 
of  the  British  Association  at  Edinburgh  (1892),  from 
which  the  following  sentences  are  quoted  : — 

"  If  we  draw  a  line  completely  round  the  globe,  crossing 
the  Atlantic  basin  at  its  shallowest,  between  Cape  Verde 
and  Cape  San  Roque,  and  continued  in  the  direction  of 
Japan,  where  the  Pacific  is  at  its  deepest,  as  the  trace  of  a 
great  circle,  we  find  that  we  have  before  us  a  crust  fold 
of  the  very  highest  and  grandest  order.  We  have  one 
mighty  continental  arch  stretching  from  Japan  to  Chili, 
broken  medially  by  the  sag  of  the  Atlantic  trough ;  and 
we  see  that  this  great  terrestrial  arch  stands  directly  opposed 
to  its  natural  complement,  the  great  trough  of  the  Pacific, 
which  is  bent  up  in  the  middle  by  the  mightiest  of  all  the 
submarine  buckles  of  the  earth-crust,  on  which  stand  the 
oceanic  islands  of  the  Central  Pacific. 

"The  course  of  this  line  which  we  have  indicated  as 
forming  our  grandest  terrestrial  fold  returns  upon  itself. 
It  is  an  endless  fold,  an  endless  band.  .  .  . 

"Such  an  endless  fold,  again,  must  have  an  endless 
septum,  which  in  the  nature  of  things  must  cross  it  twice. 
Need  I  point  out  .  .  .  that  if  we  unite  the  Old  and  New 
Worlds  and  Australia  with  their  intermediate  sags  of  the 
Atlantic  and  Indian  Oceans  as  one  imperial  earth-arch, 
and  regard  the  unbroken  watery  expanse  of  the  Pacific  as 
its  complementary  depression,  the  circular  coastal  band  of 
contrary  surface  flexure  which  lies  between  them  should 
constitute  the  moving  master  septum  of  the  present  earth- 
crust?  This  is  the  'volcanic  girdle  of  the  Pacific,'  our 
'  terrestrial  ring  of  fire.' " 

The  great  volcanic  belts,  then,  will  run  parallel 
with  our  main  coast-lines,  forming  the  septa  of  the 
great  continent-building  folds.  Other  belts  will  lie 
along  the  septa  of  the  mountain  uplifts,  giving  rise 


208     SCIENTIFIC   STUDY   OF  SCENERY 

to  lines  of  volcanoes  bordering  mountain  uplifts,  or 
will  cause  the  formation  of  volcanoes  along  the 
fissures  which  break  up  the  monoclinal  folds  of  a 
plateau  region. 

Turning  now  to  consideration  of  the  manner  in 
which  the  material  is  brought  to  the  surface,  either 
in  a  molten  or  in  a  fragmental  condition,  we  are  at 
once  struck  with  the  active  part  played  by  steam  in 
many  volcanic  eruptions.  The  immense  volumes  of 
steam  which  are  sent  forth  from  Vesuvius  during  an 
eruption,  which  spread  in  the  air  with  an  outline 
resembling  that  of  a  stone  pine,  have  long  been 
familiar ;  and  similar  phenomena  presented  by  other 
volcanoes  prove  that  superheated  water  exists  in  the 
rocks  below  the  earth's  surface  to  a  considerable 
extent,  and  this,  when  pressure  is  removed,  is  flashed 
into  steam.  This  steam  is  capable  of  exercising 
great  power  in  raising  rocks,  and  it  is  obvious  that 
much  of  the  fragmental  matter  is  hurled  out  of 
volcanoes  as  the  result  of  explosions  of  steam, 
though  it  is  not  quite  so  clear  that  molten  rock  is 
forced  out  by  the  same  agent.  Nevertheless  a  large 
number  of  observed  facts  go  to  prove  that  this  does 
actually  occur.1 

The  importance  of  steam  as  a  factor  in  producing 
volcanic  phenomena  is,  perhaps,  best  shown  by  the 
observations  made  by  Mr.  E.  Whymper  in  the  Andes. 
When  on  the  top  of  Chimborazo  he  witnessed  an 
eruption  of  Cotopaxi. 

"At  5.40  a.m.  two  puffs  of  steam  were  emitted,  and  then 
there  was  a  pause.  At  5.45  a  column  of  inky  blackness 

1  On  this  subject  the  reader  may  consult  Professor  Judd's  work  on 
Volcanoes,  chap.  ii. 


VOLCANOES  209 

began  to  issue,  and  went  up  straight  into  the  air  with  such 
prodigious  velocity  that  in  less  than  a  minute  it  had  risen 
20,000  feet  above  the  rim  of  the  crater.  .  .  .  The  top  of 
the  column  .  .  .  was  nearly  40,000  feet  above  the  level 
of  the  sea.  At  that  elevation  it  encountered  a  power- 
ful wind  blowing  from  the  east,  and  was  rapidly  borne 
towards  the  Pacific,  remaining  intensely  black,  seeming  to 
spread  very  slightly,  and  presenting  the  appearance  of  a 
gigantic  ~|  drawn  upon  an  otherwise  perfectly  clear  sky."1 

The  column  was  formed  of  steam  mixed  with  the 
volcanic  fragments,  and  Mr.  Whymper  calculates 
"  that,  at  least,  two  millions  of  tons  must  have  been 
ejected  during  this  eruption."  On  another  occasion, 
when  encamped  on  Cayambe,  he  "  saw  Cotopaxi 
pouring  out  a  prodigious  volume  of  steam,  which 
boiled  up  a  few  hundred  feet  above  the  rim  of  its 
crater,  and  then,  being  caught  by  a  south-westerly 
wind,  was  borne  towards  the  north-east,  almost  up 
to  Cayambe.  The  bottom  of  this  cloud  was  about 
5000  feet  above  us ;  it  rose  at  least  a  mile  high,  and 
spread  over  a  width  of  several  miles.  ...  I  estimate 
that  on  this  occasion  we  saw  a  continuous  body  of 
not  less  than  sixty  cubic  miles  of  cloud  formed  from 
steam.  If  this  vast  volume,  instead  of  issuing  from 
a  free  vent,  had  found  its  passage  barred,  itself 
imprisoned,  Cotopaxi  on  that,  morning  might  have 
been  effaced,  and  the  whole  continent  might  have 
quivered  under  an  explosion  rivalling  or  surpassing 
the  mighty  catastrophe  at  Krakatoa."2 

But  though  steam  clearly  plays  the  principal  part 

1  The  eruption  is  also  of  interest  as  bearing  on  the  formation  of 
stratus  clouds. 

2  WHYMPER,  E.,  Travels  amongst  the  Great  Andes  of  the  Equator^ 
chaps,  vii.  and  xviii. 

P 


210     SCIENTIFIC   STUDY   OF   SCENERY 

in  many  volcanic  eruptions,  there  are  many  other 
cases  where  its  action  is  as  clearly  secondary,  and 
some  other  agent  must  be  sought  which  is  capable  of 
raising  rock  from  the  earth's  interior. 

In  areas  where  we  find  the  rocks  affected  by 
monoclinal  faults  we  frequently  find  extensive  sheets 
of  lava  which  yield  evidence  of  having  welled  up 
from  the  interior  and  spread  out  with  a  tranquillity 
very  far  removed  from  the  explosive  violence  of 
ordinary  volcanic  eruptions,  as,  for  instance,  in  the 
plateau  region  of  the  western  territories  of  North 
America.  We  have  already  seen  that  a  region  like 
that  plateau  region  is  composed  of  blocks  tilted  at 
various  angles  as  though  they  had  sagged  down 
into  a  liquid  mass  beneath,  and  it  is  probable  that 
during  the  process  of  faulting  some  of  the  molten 
matter  below  has  been  squeezed  out  through  the 
cracks  and  spread  tranquilly  over  the  earth's  surface 
above  the  fissure.  Baron  von  Richthofen  first  main- 
tained that  such  massive  eruptions,  as  he  named 
them,  or  fissure  eruptions,  as  they  are  sometimes 
termed,  had  occurred. 

It  is,  of  course,  possible  that  material  may  be 
brought  up  by  a  combination  of  the  two  processes, 
the  sagging  action  of  the  earth's  crust  being  aided 
by  the  presence  of  superheated  water  in  the  molten 
rock. 

We  have  now  considered  the  various  processes 
which  are  necessary  for  the  production  of  volcanoes, 
and  may  proceed  to  the  consideration  of  the  general 
character  of  the  accumulations  which  are  built  up  as 
the  result  of  volcanic  action. 

The  nature  of  the  hills  and  plateaux  which  are 
formed  by  volcanic  agency  depends  primarily  upon 


VOLCANOES  211 

the  character  of  the  emitted  and  extruded  material, 
the  violence  of  the  action,  and  the  character  of  the 
vents. 

It  has  already  been  noted  that  material  is  brought 
out  from  volcanic  vents  in  a  molten  or  in  a  fragmental 
condition,  and  accordingly  any  volcano  may  be 
entirely  formed  of  material  in  one  or  other  of  these 
conditions  or  of  the  two  kinds  of  material  in  vary- 
ing proportions.  Commencing  with  the  consideration 
of  volcanic  hills  which  are  entirely  composed  of 
consolidated  molten  rock,  we  shall  find  that  the 
outline  of  the  hill  very  largely  depends  upon  the 
condition  in  which  the  molten  matter  existed  when 
it  was  extruded.  We  have  seen  that  molten  rocks 
may  be  divided  into  two  main  groups,  the  acid  and 
the  basic  rocks,  and  that  the  latter  are  on  the  whole 
in  a  condition  which  enables  them  to  flow  further 
from  the  point  or  line  of  emission  than  the  former, 
and  the  height  of  volcanoes  formed  of  basic  lavas  is 
generally  less  when  compared  with  the  circumference 
than  that  of  those  composed  of  acid  lavas.  Many 
acid  lavas,  indeed,  well  up  in  a  condition  so  viscid 
that  they  form  a  dome-shaped  elevation  covering  the 
orifice,  and  marked  with  rugosities  much  resembling 
the  products  of  a  guttering  candle.  The  reader  will 
find  descriptions  of  such  domes,  with  illustrations,  in 
the  fifth  chapter  of  Prof.  Judd's  Volcanoes.  One  of 
the  best  examples  is  the  Puy  de  Sarcoui  in  the  Au- 
vergne  district,  of  which  the  late  Mr.  Poulett  Scrope1 
writes  that  "  in  figure  it  is  completely  a  flattened  and 
rather  elongated  hemisphere,  and  is  aptly  compared 
by  the  mountain-shepherds  to  a  kettle  placed  bottom 
upwards."  Basic  rocks  often  flow  for  a  considerable 

1  ScROPEj  G.  P.,  The  Geology  and  Volcanoes  of  Central  France* 


212     SCIENTIFIC   STUDY   OF   SCENERY 

distance  from  the  point  of  extrusion  of  the  lavas. 
Mr.  Poulett  Scrope  suggested  that  the  plain  of  the 
Malpais  in  Mexico,  which  has  a  slope  of  about  6°, 
was  formed  by  extrusion  of  sheets  of  lava  from 
points  near  its  centre,  each  of  these  sheets  gradually 
thinning  away  from  its  source  and  thus  giving  rise  to 
a  sloping  surface.  More  striking  examples,  however, 
are  furnished  by  the  four  great  volcanoes  of  Hawaii, 
namely  Mauna  Loa,  Mauna  Kea,  Kilauea,  and 
Hualalai.  An  admirable  monograph  of  these 
volcanoes  from  the  pen  of  Captain  C.  E.  Button  has 
appeared  in  the  Monographs  of  the  U.S.  Geological 
Survey.1  The  mountains  are  composed  of  lava  flows 
of  a  basaltic  character,  sheet  lying  above  sheet,  and 
there  is  a  general  absence  of  fragmental  matter. 
Mauna  Kea  and  Mauna  Loa  approach  14,000  feet  in 
height,  but  "  deep  sea  soundings  in  the  vicinity  have 
recently  disclosed  the  fact  that  these  volcanic  piles 
are  only  the  summits  of  gigantic  masses  rising 
suddenly  from  the  bottom  of  the  Pacific.  .  .  .  Mauna 
Loa  and  Mauna  Kea,  referred  to  their  true  bases  at 
the  bottom  of  the  Pacific,  are  .  .  .  mountains  not  far 
from  30,000  feet  in  height."  Of  the  two  Mauna  Loa 
is  remarkable  not  only  for  its  size — it  "  is  certainly 
the  king  of  modern  volcanoes,  no  other  in  the  world 
approaches  it  in  the  vastness  of  its  mass  or  in  the 
magnitude  of  its  eruptive  activity" — but  also  for  its 
symmetrical  outline  and  the  gentle  slopes  of  its  sides, 
which  attain  an  angle  not  greater  than  6°.  The 
mountain  is  marked  by  the  existence  of  a  remarkable 
crateriform  cavity  at  its  summit,  to  which  allusion 
will  be  made  subsequently ;  but  this  does  not  modify 
the  general  outline  of  the  mountain,  which  appears 

1  DUTTON,  C.  E.,  Rept.  U.S.  Geological  Survey,  1822-3. 


VOLCANOES  213 

to  be  due  to  the  gradual  thinning  out  of  the  various 
lava  flows  issuing  from  round  this  central  point. 
As  denudation  has  produced  little  effect  upon  this 
active  volcano,  we  get  an  example  of  the  true  outline 
of  a  volcanic  mountain  formed  by  gradual  piling  up 
lava  flows,  sheet  over  sheet,  which  is  a  convex  curve, 
here  approaching  to  flatness  on  account  of  the  great 
distance  to  which  the  individual  lava  streams  have 
flowed  ;  while  in  the  hills  formed  of  more  viscid  acid 
lavas  the  curve  is  still  a  convex  one,  but  very  much 
more  pronounced,  owing  to  the  limited  distance  to 
which  the  lava  has  flowed  from  the  point  of  its 
extrusion.  When  the  volcanic  hill  is  largely  com- 
posed of  fragmental  material  the  structure  will  be 
different.  If  the  volcano  is  a  simple  one,  built  up  by 
ejection  of  fragmental  material  round  a  single  vent, 
a  conical  hill  will  result,  but  the  outline  of  the  hill  is 
not  that  of  a  true  cone.  Professor  Milne1  has  ex- 
plained the  reason  for  the  existence  of  the  actual 
outlines  possessed  by  cinder-cones,  i.e.,  cones  formed 
of  ejected  fragmental  material,  and  I  have  already 
referred  to  his  work  when  discussing  the  slope  of 
screes.  He  finds  that  many  volcanoes  built  up  of 
fragmental  materials  possess  a  surface  "which  would 
be  produced  by  a  simple  logarithmic  curve  revolving 
about  an  axis — consequently  such  a  heap  would  have 
a  slope  diminishing  from  the  top  to  the  bottom  " — 
thus  generally  resembling  the  curve  produced  by 
stream  erosion.  This  curvature,  according  to  Milne, 
would  be  produced  by  (i)  "  the  tendency  of  a  self- 
supporting  heap,  under  the  influence  of  its  own 

1  MILNE,  J.,  "On  the  Form  of  Volcanoes,"  Geol.  Mag.,  Dec.  2, 
vol.  v.,  p.  337  ;  and  "Further  Notes  upon  the  Form  of  Volcanoes," 
ibid.,  Dec.  2,  vol.  vi.,  p.  506. 


2i4    SCIENTIFIC   STUDY   OF   SCENERY 

weight,  to  spread  outwards  at  the  base — this  would 
tend  to  give  a  logarithmic  curvature "  ;  (ii)  "  the 
tendency  during  the  building  up  of  a  mountain  of 
the  larger  particles  to  roll  further  than  the  smaller 
ones";  (iii)  the  action  of  denudation.  As  he  has 
examined  many  volcanoes  in  which  the  material  is 
seldom  found  at  a  less  angle  than  its  proper  angle  of 
repose,  he  maintains  that  denudation  cannot  have 
played  a  very  important  part  in  determining  the 
slope  of  those  particular  volcanoes,  which  must 
therefore  owe  their  outline  to  the  first  two  causes. 
Milne  further  notes  that  any  hard  core  of  a  volcano, 
such  as  may  be  produced  by  ribs  of  once  molten 
rock  consolidated  in  cracks,  will  tend  to  contract 
the  base  of  the  mountain  as  compared  with  its 
height,  just  as  the  shape  of  a  pile  of  sand  poured 
upon  a  table  will  be  altered  if  we  first  place  a  small 
box  upon  the  table. 

It  would  appear,  then,  that  the  shape  of  a  sym- 
metrical volcanic  hill  formed  round  a  central  orifice 
will  be  that  of  a  plano-convex  mass,  with  a  circular 
line  around  the  base,  if  the  volcano  be  formed  of 
emission  of  molten  material,  but  that  this  will  be 
replaced  by  a  circular  mass,  whose  cross  section 
shows  two  logarithmic  curves,  ever  increasing  in 
steepness  towards  the  summit  of  the  hill  where  they 
meet,  when  the  hill  is  formed  by  accumulation  of 
ejected  fragments.  (See  Fig.  35  «.) 

We  have  now  to  consider  various  causes  which 
give  rise  to  complications  in  the  outline  and  structure 
of  volcanoes,  and  may  in  the  first  place  take  into 
account  the  effect  which  is  produced  upon  the 
appearance  of  the  volcano  owing  to  the  character 
of  the  crater.  It  has  been  seen  that  in  the  case  of 


VOLCANOES 


215 


volcanoes  built  up  by  emission  of  lava,  the  lava  may 
entirely  seal  up  the  orifice  from  which  the  emission 
has  taken  place,  so  that  no  external  sign  of  the 
orifice  is  visible.  When  volcanic  hills  are  formed 


FIG.  35. 

a  Outline  of  volcano  formed  of  fragmental  rock  piled  round  a 
central  orifice. 

b  Outline  of  volcano  truncated  by  paroxysmal  outburst.  The 
dotted  line  shows  former  height  of  hill. 

c   Cross-section  through  a  Hawaiian  volcano,  with  caldera. 

d  Volcano  of  type  b,  with  inner  crater  built  up  inside  truncated 
crater. 

e  Compound  volcano  formed  across  two  vents  (indicated  by  dotted 
lines).  The  portion  above  the  right-hand  line  has  been  removed  by 
paroxysmal  explosion  or  engulfment. 

of  fragmental  material,  however,  some  of  the 
material  falls  back  towards  the  orifice,  and  a 
hollow  is  formed  around  the  orifice  like  an  inverted 
cone,  though  having  its  slope  determined  in  the  same 
manner  as  the  outer  slopes  ;  this  hollow  is  the  crater. 
When  a  cone  is  built  up  as  the  result  of  ejection  of 


216     SCIENTIFIC   STUDY   OF   SCENERY 

fragmental  materials,  emitted  with  no  great  violence, 
the  crater  need  not  be  very  large,  and  the  diameter 
of  its  upper  rim  need  not  therefore  greatly  modify 
the  general  conical  form  of  the  hill,  as  seen  from 
a  distance.  The  actual  apex  of  the  cone  will  appear 
to  be  cut  off,  as  shown  in  the  case  of  the  cone  of 
Cotopaxi,  or  that  of  Fusiyama,  the  latter  so  well 
known  from  representations  on  Japanese  fans  and 
other  works  of  art,  but  the  missing  portion  will  form 
a  very  small  portion  of  the  entire  cone,  and  merely 
gives  the  effect  of  a  blunted  point.  In  some  circum- 
stances, however,  the  crater  becomes  of  very  great 
importance  as  modifying  the  general  outline  of  the 
volcano ;  this  is  specially  well  seen  where  eruptions 
of  paroxysmal  violence  have  occurred.  In  many 
early  accounts  of  eruptions  of  excessive  violence 
it  is  stated  that  the  upper  part  of  the  volcano  fell  in, 
but  there  is  little  doubt  that,  as  in  the  case  of 
observed  recent  paroxysmal  eruptions,  it  was  not 
engulfed,  but  blown  into  the  air  in  small  fragments, 
which  were  dispersed  far  and  wide  around  the 
volcanic  hill.  An  explosion  of  this  character  may 
give  rise  to  a  truncated  cone,  containing  a  gigantic 
basin-shaped  crater  within  (see  Fig.  35  b}\  the  interior 
hollow  of  Vesuvius  before  the  great  eruption  which 
destroyed  Pompeii  and  Herculaneum  was  of  this 
nature.  The  upper  rim  of  the  truncated  volcano 
may  be  fairly  regular,  or  may  be  of  great  irregularity, 
when  from  some  points  of  view  the  volcanic  character 
of  the  hill  will  be  entirely  concealed.  Should  the 
paroxysmal  eruption  which  produced  truncation  be 
succeeded  by  comparatively  feeble  outbursts,  allow- 
ing of  fresh  accumulation  of  ejected  fragments,  a 
new  cone  will  be  built  up  within  the  old  crater- 


VOLCANOES  217 

ring,  and  a  cone  within  a  cone  so  formed,  as  has 
happened  with  Vesuvius,  where  the  modern  cone  is 
half  surrounded  by  the  partly  destroyed  old  crater- 
ring,  the  surviving  portion  of  which  is  known  as 
Monte  Somma.  This  type  is  illustrated  in  Fig.  35  d. 

Besides  the  ordinary  craters,  formed  by  rolling 
back  of  fragments  to  the  orifice,  and  those  due  to 
paroxysmal  explosions,  there  is  another  class  of 
crater,  apparently  due  to  sinking  of  the  upper 
portion  of  the  volcano.  This  class  is  well  repre- 
sented in  the  volcanoes  of  Hawaii,  and  the  craters 
of  this  type  are  spoken  of  as  calderas.  (See  Fig. 
35  c.}  The  best  known  is  that  of  Kilauea,  though 
another  occurs  on  the  top  of  Mauna  Loa,  and  a 
gigantic  though  somewhat  irregular  one  on  the 
summit  of  Haleakala,  on  the  island  of  Maui.  The 
caldera  of  Kilauea  is  of  a  general  elliptical  shape, 
with  a  longer  diameter  of  three  and  a  half  miles, 
and  a  shorter  one  of  two  and  a  half  miles,  sur- 
rounded by  precipitous  cliffs  and  varying  in  altitude 
from  300  to  over  700  feet,  according  to  the  state  of 
its  floor.  Haleakala  possesses  a  V-shaped  caldera, 
one  limb  of  which  is  seven,  and  the  other  eight  miles 
long ;  the  precipitous  walls  rise  to  a  height  of  1 500 
to  2000  feet  above  a  plain  from  three  to  five  miles 
wide.  Haleakala  is  no  longer  active,  but  the  nature 
of  the  eruptions  of  Kilauea  is  well  known.  When 
empty  the  crater-floor  is  about  700  feet  below  the 
rim.  It  consists  of  an  undulating  mass  of  black 
rock,  with  a  large  pile  of  rocks  near  the  centre. 
From  it  issue  jets  of  steam,  and  where  a  crack  occurs, 
the  red  glow  of  the  molten  rock  is  seen.  But  at 
times  the  molten  rock  gradually  rises  towards  the 
rim  of  the  crater  until  it  is  tapped  at  some  point 


218     SCIENTIFIC   STUDY   OF   SCENERY 

lower  down  the  mountain,  when  the  lava  wells  tran- 
quilly out  and  flows  for  great  distances  until  the  floor 
of  the  crater  is  once  more  reduced  to  its  normal 
level.  Button  quotes  the  following  description  given 
by  Lieutenant  Wilkes  of  the  appearances  of  the 
crater  when  occupied  by  molten  rock  : — 

"All  usual  ideas  of  volcanic  craters  are  dissipated  upon 
seeing  this.  There  is  no  elevated  cone,  no  igneous  matter 
or  rocks  ejected  beyond  the  rim.  The  banks  appear  as  if 
built  of  massive  blocks,  which  are  in  places  clothed  with 
ferns  nourished  by  the  issuing  vapours.  What  is  wonder- 
ful in  the  day  becomes  ten  times  more  so  at  night.  The 
immense  pool  of  cherry-red  liquid  lava  in  a  state  of  violent 
ebullition  illuminates  the  whole  expanse  and  flows  in  all 
directions  like  water,  while  the  illuminated  cloud  hangs 
over  it  like  a  vast  canopy." 

There  is  no  doubt  that  these  calderas  have  origin- 
ated in  a  manner  different  from  that  of  ordinary 
volcanic  craters,  and  Button  gives  reasons  for  sup- 
posing that  they  are  due  to  successive  sinking  of 
slices  of  the  walls  along  the  lines  of  fissure  into  the 
molten  mass  below,  a  process  which  is  still  going 
on,  and  has  given  rise  to  a  series  of  fault  scarps  and 
terraces  around  the  sides  of  the  crater.  (See  Fig. 

35*0 

Further  complications  in  the  form  of  volcanoes 
may  be  produced  by  the  resistance  of  two  or  more 
adjacent  orifices  when  the  materials  ejected  from 
these  coalesce  to  form  a  compound  mountain,  as  has 
occurred  in  the  case  of  the  double  Monti  Rossi  on 
the  outskirts  of  Etna.  Sartorius  von  Waltershausen 
has  given  reasons  for  supposing  that  Etna  itself 
has  been  built  up  round  two  distinct  axes  of 


VOLCANOES  219 

eruption,  one  coinciding  with  the  present  summit, 
the  other  being  situated  about  the  centre  of  the 
remarkable  crateriform  Val  del  Bove.1  Owing  to 
the  peculiar  conditions  we  do  not  find  two  coalesced 
hills,  but  a  deep  depression  around  the  second  axis, 
namely,  this  Val  del  Bove.  It  is  not  clear  how  it 
was  formed.  Lyell  supposes  it  to  have  been  pro- 
duced by  paroxysmal  outbursts,  but  Button  compares 
it  with  the  calderas  of  the  Hawaiian  volcanoes.  (See 
Fig.  35  e,  and  Lyell,  loc.  cit.,  Fig.  71.) 

There  are  many  minor  causes  which  tend  to 
produce  a  want  of  symmetry  in  volcanic  hills.  The 
prevailing  wind  may  cause  more  material  to  fall  on 
the  leeward  side  of  a  cone  built  up  of  fragmental 
materials  than  on  the  windward  side,  and  accord- 
ingly the  edge  of  the  crater  will  be  higher  on  one 
side  than  on  the  other,  and  in  the  case  of  small 
cones  an  appreciable  amount  of  distortion  may 
be  thus  produced.  Again,  parasitic  cones  are  often 
formed  upon  the  sides  of  larger  volcanic  hills,  and 
may  interrupt  the  regularity  of  outline,  though  if 
the  primary  hill  be  very  large  and  the  parasitic  cones 
small,  their  effect  at  a  distance  will  not  be  material  in 
influencing  the  nature  of  the  outline  of  the  hill. 
One  side  of  a  volcanic  cone  formed  of  fragmental 
materials  may  be  breached  by  a  lava-flow,  which 
finds  it  easier  to  break  through  the  mass  of  more 
or  less  incoherent  material  than  to  rise  to  the  lip 
of  the  crater.  A  number  of  small  cones — the  puys 
of  Auvergne — are  breached  in  this  way,  leaving  a 
semicircular  cliff  around  the  source  of  the  lava-flow. 

The  nature  of  the  lava  itself  often  produces 
marked  effect  upon  the  scenery  of  a  volcanic  district. 

1  See  LYELL,  Sir  C.,  Principles  of  Geology ,  vol.  ii.,  chap.  xxvi. 


220    SCIENTIFIC   STUDY   OF   SCENERY 

Owing  to  the  relative  abundance  of  alkaline  com- 
pounds in  the  lavas  and  ashes,  they  frequently  form 
fertile  soils  upon  weathering,  and  many  ancient 
lavas  are  covered  by  a  luxuriant  growth  of  vegeta- 
tion, but  the  recent  flow  often  presents  a  black, 
forbidding  surface,  the  nature  of  which  will  vary 
according  to  the  character  of  the  lava,  as  is  very  well 
seen  in  the  case  of  the  Hawaiian  lavas,  as  described 
by  Button.  Two  forms  of  lava  are  found  in  Hawaii, 
known  to  the  natives  by  the  names  of  "pahoehoe"  and 
"aa."  The  former  is  thus  described  by  Button  : — 

"  Imagine  an  army  of  giants  bringing  to  a  common 
dumping-ground  enormous  cauldrons  of  pitch  and 
turning  them  upside  down,  allowing  the  pitch  to  run 
out,  some  running  together,  some  being  poured  over 
preceding  discharges,  and  the  whole  being  finally 
left  to  solidify.  The  individuality  of  each  vessel-full 
of  pitch  might  be  half  preserved,  half  obliterated. 
The  surface  of  the  entire  accumulation  would  be 
embossed  and  rolling,  by  reason  of  the  multiplicity 
of  the  component  masses,  but  each  mass  by  itself 
would  be  slightly  wrinkled,  yet  on  the  whole  smooth, 
involving  no  further  impediment  to  progress  over 
it  than  the  labour  of  going  up  and  down  the 
smooth-surfaced  hummocks."  It  is  produced  by  the 
surface  solidifying  while  the  interior  of  the  flow  is 
still  liquid.  The  superficial  crust  cracks  in  numerous 
places,  and  little  squirts  of  the  fluid  beneath  are 
ejected  through  the  fissures,  which  spread  out  and 
become  quickly  cooled,  when  the  process  is  repeated. 
The  "  aa "  "  consists  mainly  of  clinkers,  sometimes 
detached,  sometimes  partially  agglutinated  together 
with  a  bristling  array  of  sharp,  jagged,  angular  frag- 
ments of  a  compact  character  projecting  up  through 


VOLCANOES  221 

them.  The  aspect  of  one  of  these  "  aa  "  streams  is 
repellent  to  the  last  degree,  and  may  without 
exaggeration  be  termed  horrible.  For  one  who  has 
never  seen  it,  it  is  difficult  to  conceive  such  super- 
lative roughness."  The  lava  forming  "  aa  "  has  the 
same  composition  as  that  which  gives  rise  to 
"  pahoehoe,"  and  the  difference  is  due  to  difference  in 
the  nature  of  the  cooling.  The  mass  of  lava  which 
forms  "aa"  is  in  a  condition  approaching  consolidation, 
and  it  moves  very  slowly.  During  the  movement 
"crushing  strains  of  great  intensity  are  set  up 
throughout  the  entire  mass,  and  its  behaviour 
conforms  strictly  to  that  of  viscous  bodies.  The 
superficial  portions  in  part  yield  plastically  to  the 
strains,  in  part  yield  by  crushing,  splintering,  and 
fissuring.  The  result  is  a  chaos  of  angular  frag- 
ments." 

It  has  already  been  noted  that  difference  of  com- 
position determines  different  rates  of  flow,  and  ac- 
cordingly the  surfaces  of  different  kinds  of  lava  vary 
considerably,  and  we  have  every  gradation,  from  the 
comparatively  smooth  surfaces  of  some  lavas,  through 
the  ropy  and  coiled  tops  of  others,  to  the  rough 
accumulation  of  clinkers  which  form  the  dreary  "aa" 
of  Hawaii. 

A  few  remarks  concerning  the  atmospheric  effects 
produced  during  volcanic  eruptions  may  not  be  out 
of  place.  It  is  well  known  that  the  smoke  and 
flames  of  popular  descriptions  of  volcanic  eruptions 
are  not  actually  due  to  combustion,  the  "smoke"  being 
really  dense  volumes  of  discharged  steam,  which 
condenses  into  thick  clouds,  often  darkened  by  the 
mixture  of  myriads  of  solid  particles,  while  the 
appearance  of  "flame"  is  due  to  the  reflection  of 


222     SCIENTIFIC   STUDY   OF   SCENERY 

the  molten  lava  upon  the  clouds  of  condensed  vapour. 
The  condensed  vapour  usually  issues  as  a  vertical 
column,  until  it  reaches  a  considerable  altitude,  when 
it  spreads  out  as  cumulus  or  stratus  clouds,  or 
varieties  of  these.  Reference  has  already  been  made 
to  the  "stone-pine"  arrangement  of  the  Vesuvian 
vapour,  and  also  to  the  remarkable  mass  ejected 
from  Cotopaxi,  recorded  by  Whymper,  which  at  first 
formed  a  vertical  column,  then  bent  suddenly  at  right 
angles  and  proceeded  for  miles  in  one  direction  as  a 
horizontal  layer.  The  importance  of  the  spread  of 
minute  particles  of  solid  material  through  the  atmo- 
sphere, in  producing  effects  upon  the  nature  of  the 
sunset  colours,  as  shown  in  the  case  of  the  great 
eruption  of  Krakatoa,  has  also  been  alluded  to  in 
a  previous  chapter. 

In  some  cases  there  is  actual  combustion  of  gas, 
usually  giving  a  pale,  lambent  flame,  which  produces 
no  very  marked  effect  upon  the  scene. 

The  scenic  effects  of  different  eruptions  will  vary 
considerably ;  but  a  good  idea  of  one  may  be  ob- 
tained by  reading  the  following  description  of  an 
eruption  of  Kilauea  in  1883,  witnessed  by  the  Rev. 
W.  Ellis,  whose  description  of  the  scene  is  quoted  by 
Button,  it  being  noted  that  some  terms  used  in  the 
description  are  used  in  a  very  general  sense.  After 
describing  the  caldera,  he  proceeds  as  follows : — 

"  The  bottom  was  covered  with  lava,  and  the  south-east, 
north-east,  and  northern  parts  were  one  vast  flood  of 
burning  matter  in  a  state  of  terrific  ebullition,  rolling  to 
and  fro  its  fiery  surge  and  flaming  billows.  Fifty-one 
conical  islands  of  varied  form  and  size,  containing  as 
many  craters,  rose  either  around  the  edge  or  from  the 
surface  of  the  burning  lake,  twenty-two  constantly  emitting 


VOLCANOES  223 

columns  of  grey  smoke  or  pyramids  of  brilliant  flame,  and 
several  of  these  at  the  same  time  vomiting  from  their 
ignited  mouths  streams  of  lava,  which  rolled  in  blazing 
torrents  down  their  black  indented  sides  into  the  boiling 
mass  below.  .  .  .  The  grey,  and  in  some  places  apparently 
calcined,  sides  of  the  great  crater  before  us,  the  fissures 
which  intersected  the  surface  of  the  plain  on  which  we 
were  standing,  the  long  banks  of  sulphur  upon  the  opposite 
side  of  the  abyss,  the  dense  columns  of  vapour  and  smoke 
that  rose  at  the  north  and  south  end  of  the  plain,  together 
with  the  range  of  steep  rocks  by  which  it  was  surrounded, 
probably  in  some  places  300  or  400  feet  in  perpendicular 
height,  presented  an  immense  volcanic  panorama,  the  effect 
of  which  was  greatly  augmented  by  the  constant  roaring 
of  the  vast  furnaces  below.  .  .  .  Between  nine  and  ten 
in  the  evening  the  dark  clouds  and  lava  fog,  that  since 
the  setting  of  the  sun  had  hung  over  the  volcano,  gradually 
cleared  away;  and  the  fires  of  Kilauea,  darting  their  fierce 
light  athwart  the  midnight  gloom,  unfolded  a  sight  terrible 
and  sublime  beyond  all  we  had  yet  seen. 

"The  agitated  mass  of  liquid  lava,  like  a  flood  of 
melted  metal,  raged  with  tumultuous  whirl.  The  lively 
flame  that  danced  over  its  undulating  surface,  tinged  with 
sulphurous  blue  or  glowing  with  mineral  red,  cast  a  broad 
glare  of  dazzling  light  on  the  indented  sides  of  the  in- 
sulated craters,  whose  roaring  mouths,  amidst  rising  flames 
and  eddying  streams  of  fire,  shot  up  at  frequent  intervals, 
with  very  loud  detonations,  spherical  masses  of  fusing  lava 
or  bright,  ignited  stones." 

The  remarkable  gentleness  of  the  slopes  of  the 
Hawaiian  volcanoes  has  already  been  noticed.  If 
lavas  possessing  the  liquidity  of  the  Hawaiian  lavas 
issued  for  a  considerable  distance  along  the  length 
of  a  fissure,  instead  of  from  isolated  points,  the 
flatness  would  be  increased,  and  the  products  of 


224    SCIENTIFIC   STUDY   OF   SCENERY 

vulcanicity  instead  of  forming  groups  of  hills  would 
give  rise  to  extensive  horizontal,  or  nearly  horizontal, 
plateaux.  The  massive  eruptions  of  Richthofen  are 
supposed  to  have  produced  plateaux  of  this  nature, 
of  which  the  best  known  are  those  of  the  Western 
Territories  of  North  America,  of  the  Deccan  of  India, 
of  the  Western  Isles  of  Scotland,  and  the  north-east 
portion  of  Ireland,  and  of  various  islands  to  the 
north  of  the  Eurasian  continent.  Should  the  ground 
be  uneven  at  the  commencement  of  volcanic  activity, 
the  hollows  will  be  rilled  with  lava,  and  subsequent 
streams  will  flow  over  the  comparatively  even  surface 
thus  produced,  sealing  up  the  fissures  from  which  the 
lava  issued,  and  giving  rise  to  stretches  of  flat  country, 
through  which  rivers  may  flow  in  deep  gorges  and 
canons,  sufficiently  narrow  to  prevent  any  inter- 
ference with  the  general  flatness  of  the  prospect. 
Here  is  a  description  of  one  of  these  plateaux  by 
the  Snake  River  in  Idaho,  from  the  facile  pen  of  Sir 
Archibald  Geikie1  :— 

"We  emerged  from  the  mountains  upon  the  great  sea 
of  black  lava,  which  seems  to  stretch  inimitably  west- 
wards. With  minds  keenly  excited  by  the  incidents  of 
the  journey,  we  rode  for  hours  by  the  side  of  that  apparently 
boundless  plain.  Here  and  there  a  trachytic  spur  pro- 
jected from  the  hills,  succeeded  now  and  then  by  a  valley 
up  which  the  black  flood  of  lava  would  stretch  away  unto 
the  high  grounds.  It  was  as  if  the  great  plain  had  been 
filled  with  molten  rock,  which  had  kept  its  level,  and 
wound  in  and  out  along  the  bays  and  promontories  of  the 
mountain  slopes  as  a  sheet  of  water  would  have  done. 
Copious  springs  and  streams  which  issue  from  the 
mountains  are  soon  lost  under  the  arid  basalt.  The 

1  Geological  Sketches  at  Home  and  Abroad^  No.  xi. 


VOLCANOES  225 

Snake  River  itself,  however,  has  cut  out  a  deep  gorge 
through  the  basalt  down  into  the  trachytic  lavas  under- 
neath, but  winds  through  the  desert  without  watering  it. 
The  precipitous  walls  of  the  canon  show  that  the  plain  is 
covered  by  a  succession  of  parallel  sheets  of  basalt  to  a 
depth  of  several  hundred  feet.  .  .  .  Riding  hour  after  hour 
among  these  arid  wastes,  I  became  convinced  that  all 
volcanic  phenomena  are  not  to  be  explained  by  the 
ordinary  conception  of  volcanoes,  but  that  there  is  another 
and  grander  type  of  volcanic  action,  where,  instead  of 
issuing  from  a  local  vent,  whether  or  not  along  a  line  of 
fissure,  and  piling  up  a  cone  of  lava  and  ashes  around  it, 
the  molten  rock  has  risen  in  many  fissures,  accompanied 
by  the  discharge  of  little  or  no  fragmentary  material,  and 
has  welled  forth  so  as  to  flood  the  lower  ground  with 
successive  horizontal  sheets  of  basalt.  Recent  renewed 
examination  of  the  basalt  plateaux  and  associated  types 
in  the  west  of  Scotland  has  assured  me  that  this  view  of 
their  origin  and  connection,  which  first  suggested  itself  to 
my  mind  on  the  lava-plains  of  Idaho,  furnishes  the  true 
key  to  their  history." 

From  the  remarks  made  in  the  last  paragraph,  it 
will  be  seen  that  volcanic  action  produces  its  effect 
upon  scenery  even  in  areas  where  the  volcanic  forces 
are  no  longer  in  action,  and  we  may  briefly  consider 
this  effect. 

The  fragmental  material  ejected  from  volcanic 
vents,  on  account  of  its  porosity,  often  resists  denu- 
dation for  a  considerable  period,  as  proved  by  the 
perfection  of  the  puys  of  Auvergne,  which  are  built 
of  fragmental  material,  but  denudation  sooner  or 
later  produces  marked  effects  upon  the  accumulations 
of  an  extinct  volcano,  be  these  fragmental  or  con- 
sisting of  once  molten  rock,  The  tract  of  ground 
Q 


226     SCIENTIFIC   STUDY   OF   SCENERY 

formed  of  volcanic  ejecta  will  be  denuded  in  accord- 
ance with  the  ordinary  laws  of  denudation,  but  as 
the  volcanic  rocks  are  often  much  more  durable  than 
ordinary  stratified  rocks,  they  frequently  stand  out 
after  surrounding  rocks  have  been  worn  away,  giving 
rise  to  hills  and  plateaux.  Of  this  nature  are  many 
of  the  Western  Isles  of  Scotland.  The  portions 
which  have  escaped  denudation  may  be  covered  up 
with  sediment,  and  the  latter  may  be  again  removed 
ages  subsequently  to  its  accumulation,  once  more 
exposing  the  volcanic  mass  to  the  action  of  surface 
agencies,  and  if  they  resist  this  action  more  than  the 
surrounding  sediments,  they  may  again  be  formed 
into  hills  long  ages  after  the  extinction  of  the  volcanic 
forces  which  produced  them.  The  finest  scenery  of 
Cumbria  and  Cambria  largely  owes  its  character  to 
the  durability  of  volcanic  rocks  of  great  antiquity, 
which,  having  been  for  ages  buried,  have  once  again 
been  exposed  to  the  surface,  and  resisting  denudation 
more  than  the  surrounding  sediments,  have  stood  out 
as  hill-masses,  which  thus  owe  their  origin  to  ancient 
volcanic  action,  though  only  very  indirectly.  It  need 
hardly  be  added  that  no  traces  of  the  original  out- 
lines of  the  volcano  or  volcanoes  are  preserved  in 
these  circumstances. 

Hot  Springs  and  Geysers. — Closely  connected  with 
ordinary  volcanic  phenomena  are  those  of  many  hot 
springs,  especially  geysers,  which  are  characteristic 
of  volcanic  regions,  the  heat  being  supplied  from 
volcanic  sources.  Geysers  differ  from  other  hot 
springs  in  that  the  water  is  thrown  into  the  air  in 
the  form  of  a  fountain.  There  has  been  much  dis- 
cussion as  to  the  exact  conditions  which  are  necessary 
for  the  emission  to  take  place,  but  it  is  generally 


VOLCANOES  227 

agreed  that  superheated  water,  flashing  into  steam 
on  the  removal  of  pressure,  is  the  active  cause  of  the 
phenomenon,  and  it  is  furthermore  admitted  that  the 
water  becomes  heated  in  the  tube,  which  is  connected 
with  the  surface.  Water  gains  admission  from  the 
surface  to  the  interior  of  the  earth  in  a  volcanic 
district  until  it  reaches  a  place  where  the  temperature 
is  above  its  ordinary  boiling  point  at  no  great 
distance  below  the  surface,  frequently  in  the  lower 
portions  of  a  still  warm  lava  current  which  has  long 
solidified.  The  steam  is  forced  up  a  fissure,  and 
gradually  enlarges  the  sides  of  the  fissure,  forming 
a  pipe-shaped  cavity.  In  this  the  water  collects, 
and  the  pressure  of  the  superincumbent  water  is 
sufficient  to  prevent  the  water  below  from  boiling 
at  the  ordinary  boiling  point,  and  accordingly  it 
becomes  heated  above  ioo°C.  In  the  meantime  some 
of  the  water  above  is  evaporated  and  the  pressure 
lessened,  until  at  last  the  diminution  is  sufficient  to 
allow  the  superheated  water  to  flash  into  steam, 
which  violently  expels  the  remaining  water  in  the 
pipe  into  the  air,  causing  an  eruption  of  the  geyser. 
The  best-known  geysers  are  those  of  Iceland,  of  the 
Yellowstone  National  Park  of  North  America,  and 
of  the  northern  island  of  New  Zealand.  The  "  Old 
Faithful "  geyser  of  the  Yellowstone  Park  ejects  a 
fountain  of  water  to  a  height  of  over  100  feet  about 
every  hour.  The  fact  that  there  are  differences  in 
action  of  geysers  indicates  that  the  exact  cause  of 
eruption  is  not  always  the  same. 

Geysers  and  other  hot  springs  are  also  of  interest 
to  us  on  account  of  the  accumulations  which  are 
formed  by  their  agency.  The  hot  water  percolating 
through  igneous  rocks  is  capable  of  taking  up  various 


228     SCIENTIFIC   STUDY   OF   SCENERY 

soluble  substances,  which  it  cannot  hold  in  solution 
when  cool,  and  accordingly  the  substances  are  de- 
posited around  the  springs  in  the  form  of  sinter, 
which,  in  the  case  of  geysers,  tend  to  form  rings 
enclosing  a  crater-shaped  basin,  in  the  centre  of 
which  is  the  orifice  from  which  the  water  is  ejected, 
and  these  rings  may  be  built  up  to  some  height 
above  the  original  surface  to  form  conical  mounds 
with  the  crateriform  hollow  in  the  centre,  as  seen 
around  Old  Faithful  and  the  Giant  Geyser  of  the 
Yellowstone  Park. 

When  the  springs  issue  upon  the  slope  of  a  hill, 
the  remarkable  sinter  terraces  of  volcanic  regions  are 
formed.  The  water  flows  down  the  hill,  and  upon 
cooling  deposits  its  dissolved  material,  as  a  terrace, 
chiefly  below  the  place  from  which  it  issues,  but 
eventually  at  the  point  of  emergence,  which  may 
then  be  sealed  up,  and  the  water  will  be  compelled 
to  find  a  vent  higher  up  the  hill.  The  process  is 
repeated  again  and  again,  until  a  series  of  terraces 
are  formed  one  above  the  other  on  the  hill-side,  and 
if  a  number  of  springs  issue  along  a  line  these 
terraces  will  extend  for  considerable  distances  and 
hold  up  the  water  in  a  series  of  pools.  The  re- 
searches of  Mr.  W.  H.  Weed  have  proved  that 
certain  algae  which  are  capable  of  existing  in  hot 
water  are  largely  responsible  for  the  deposition  of 
the  dissolved  carbonate  of  lime  or  silica,  so  that  the 
process  is  not  always  a  simple  chemical  one,  but 
partly  organic.1  The  pink  and  white  terraces  of 
Rotamahana,  New  Zealand,  destroyed  by  the  great 
eruption  of  Tarawera  in  1886,  were  the  best 

1  WEED,  W.  H.,  Ninth  Annual  Report  U.S.  Geol.  Survey,  1889, 
and  American  Journal  of  Science,  vol.  xxxvii.,  p.  351. 


VOLCANOES  229 

examples  of  sinter  terraces,  but  many  exist  in  the 
Yellowstone  Park.  The  water  often  pours  from  the 
basin  of  one  terrace  into  that  of  the  one  beneath, 
and  permits  of  the  formation  of  stalagmitic  and 
stalactitic  growths,  which  often  add  to  the  remark- 
able appearance  of  the  terraces.  The  terraces  vary 
in  colour  from  the  purest  white  to  various  shades  of 
pink,  orange,  and  brown,  the  colour  being  due  to 
compounds  of  iron  mixed  with  the  lime  or  silica. 
Perhaps  the  most  impressive  are  the  marble-white 
terraces,  which  support  pools  of  pure  water  having 
its  characteristic  bright  blue  tint. 

Mud  Volcanoes. — In  many  volcanic  and  some  non- 
volcanic  areas,  various  gases  issue  from  the  earth's 
interior  and  throw  up  mas'ses  of  mud,  which  form 
cones  with  central  craters  sometimes  to  heights  of 
two  or  three  hundred  feet,  which  resemble  miniature 
volcanoes.  Small  mud-volcanoes  are  found  in  Sicily, 
but  some  of  the  most  important  occur  over  a  con- 
siderable area  in  the  basin  of  the  Lower  Indus. 

Earthquakes. — The  effects  of  earthquakes  may  be 
briefly  touched  upon  in  this  place,  as  many  earth- 
quakes are  clearly  produced  by  volcanic  action, 
though  others  are  as  obviously  not  so  caused. 
Striking  as  are  the  effects  of  earthquakes,  as  bring- 
ing about  destruction  of  life  and  property,  their 
importance  to  the  student  of  scenery  is  rather  on 
account  of  the  assistance  which  they  afford  to  other 
agents,  than  because  of  any  peculiar  features  to 
which  they  themselves  give  rise.  Besides  elevating 
and  depressing  tracts  of  country,  and  thus  assisting 
the  slow  secular  movements  of  elevation  and  de- 
pression, they  frequently  produce  extensive  gaping 
fissures,  which  may  remain  open  for  a  considerable 


23o     SCIENTIFIC   STUDY   OF   SCENERY 

period,  and  thus  initiate  new  lines  of  drainage. 
Again  they  are  often  the  cause  of  landslips,  and 
shatter  the  rock  in  such  a  way  as  to  accelerate  the 
action  of  the  weather.  They  may  give  rise  to  lakes 
by  engulfment  of  portions  of  the  earth's  crust,  or 
by  the  formation  of  barriers  owing  to  landslips,  and 
as  these  barriers  are  often  incoherent  they  may  be 
unable  to  withstand  the  pressure  of  the  water  which 
accumulates  behind  them,  when  the  temporary  lake 
will  burst,  causing  a  disastrous  flood,  during  which 
much  corrasion  and  transport  may  occur. 

Submarine  earthquakes  often  give  rise  to  earth- 
quake waves,  which  are  much  greater  than  ordinary 
wind-waves,  and  accordingly  more  destructive,  and 
these  waves  will,  therefore,  materially  assist  the 
ordinary  marine  agents  in  denuding  the  sea-coasts 
of  a  tract  of  country  which  is  affected  by  them. 
During  the  Lisbon  earthquake  of  1755,  the  earth- 
quake wave  is  stated  to  have  been  sixty  feet  high 
at  Cadiz.  Many  of  the  inland  waters  of  Europe 
were  affected  by  waves  due  to  the  same  earthquake. 

Though  the  ruin  produced  by  earthquakes  is  often 
very  apparent,  the  operation  of  the  ordinary  agents 
is  sufficient  to  heal  the  scars  due  to  earthquake 
action  in  a  comparatively  short  time,  and  accord- 
ingly, as  above  stated,  no  important  scenic  effects 
can  be  directly  ascribed  to  earthquake  action. 


CHAPTER   XIV. 
PLAINS   AND   PLATEAUX 

THE  production  of  a  comparatively  level  surface 
in  a  district  which  has  previously  been  marked 
by  very  uneven  ground,  may  be  due  either  to  denu- 
dation or  to  deposition,  or  to  a  combination  of  the 
two  processes,  and  in  these  ways  the  minor  plains 
of  the  earth's  surface  are  formed.  But  as  the  sea  is 
the  great  receptacle  of  deposit  another  event  often 
takes  place,  causing  the  formation  of  a  plain,  namely, 
the  uplift  of  the  deposits  which  formerly  existed 
upon  the  sea-bottom ;  when  this  uplift  brings  the 
deposits  above  the  surface  of  the  ocean,  and  the 
uplift  is  comparatively  equable,  a  plain  is  the  result, 
and  some  of  the  most  important  plains  which  occupy 
the  earth's  surface  have  been  produced  by  uplift  of 
marine  sediments.  The  terms  plain  and  plateau 
are  used  somewhat  vaguely.  A  plain  is  in  no  case 
absolutely  level  over  large  areas,  and  considerable 
departure  from  an  ideal  level  may  exist,  yet  the  area 
may  be  spoken  of  as  a  plain,  especially  if  it  occurs 
in  a  position  which  causes  it  to  present  a  marked 
contrast  to  an  adjoining  hill  region,  as  the  plain  of 
York,  which  is  contrasted  with  the  Yorkshire  Wolds 
on  the  one  side  and  the  moors  on  the  other.  Again, 
a  plateau  is  usually  defined  as  an  elevated  plain,  but 
the  amount  of  elevation  necessary  to  turn  a  plain 
231 


232     SCIENTIFIC   STUDY   OF   SCENERY 

into  a  plateau  cannot  be  stated,  and  the  term  plateau 
is  often  applied  to  a  tract  which  is  not  more  elevated 
than  some  other  which  would  be  termed  a  plain  ;  for 
instance,  if  a  very  extensive  tract  of  land  sloped  gently 
upwards  from  sea-level  to  a  height  of  3000  or  4000 
feet  above  the  sea,  the  whole  might  well  be  termed  a 
plain,  whereas  if  a  small,  flat  level  only  1000  to  2000 
feet  above  the  sea  was  markedly  separated  by  steep 
slopes  from  the  adjoining  low  ground,  it  would  be 
called  a  plateau.  Plateaux,  and  to  a  less  extent 
plains,  are  often  traversed  by  river  valleys  of  con- 
siderable depth,  and  as  the  process  of  erosion  goes 
on,  the  portions  left  between  the  valleys  become 
more  and  more  restricted,  and  a  plateau  will  thus  be 
carved  into  isolated  hills  often  flat-topped.  It  is,  of 
course,  impossible  to  give  any  definite  statement  of 
the  exact  amount  of  erosion  necessary  to  make  the 
term  plateau  inapplicable  to  such  a  sculptured  tract 
of  land  which  was  originally  flat. 

Any  of  the  denuding  agents,  subaerial  or  marine, 
which  are  capable  of  corrasion  and  transport,  are 
capable  of  giving  rise  to  plains  by  corrasion  in  places 
and  accumulation  in  others.  The  effects  of  wind, 
ice,  and  the  sea  will  be  considered  in  subsequent 
chapters,  and  we  may  here  note  the  effect  of  rivers 
in  producing  plains  by  corrasion  and  deposit.  It 
has  already  been  seen  that  when  a  river  has  estab- 
lished its  base-level  of  corrasion,  lateral  corrasion 
becomes  effective,  and  the  river  commences  to  cut 
sideways  at  its  curves,  giving  rise  to  flat  tracts  of 
planation,  or,  in  other  words,  plains,  which  may  be 
further  modified  by  deposition  of  alluvium  upon 
them.  It  has  also  been  indicated  that  by  lateral 
corrasion  one  river  may  tap  another,  and  in  this 


PLAINS   AND   PLATEAUX  233 

way  the  extent  of  a  river  plain  may  be  largely 
increased.  These  plains  will,  of  course,  not  be 
actually  level,  but  will  slope  gently,  though  often 
imperceptibly,  downwards  towards  the  sea.  The 
ultimate  effect  of  this  action,  if  unchecked,  would 
be  the  general  degradation  of  a  continent  by  river 
action  to  form  a  peneplain,  but  as  some  checking 
process  often  intervenes,  these  peneplains  are  always 
restricted  to  portions  of  our  continental  tracts. 

We  have  pointed  out  in  a  preceding  chapter  that, 
when  a  consequent  stream  traverses  alternating  hard 
and  soft  strata,  the  river  valley  tends  to  be  widened 
along  the  softer  strata,  and  remains  comparatively 
narrow  where  the  river  traverses  the  harder  rocks. 
Furthermore,  the  base-level  of  corrasion  will  be 
locally  reached  along  the  course  over  the  softer 
strata,  while  vertical  corrasion  still  occurs  among 
the  harder  ones,  and  small  plains  will  therefore  tend 
to  arise  over  the  softer  rocks  as  the  result  of  lateral 
corrasion,  often  possessing  a  general  elliptical  shape, 
and  dying  out  where  the  river  course  is  situated 
upon  hard  rocks  above  and  below.  It  will  be 
difficult  to  distinguish  the  alluvial  tracts  so  produced 
from  small  plains  which  have  resulted  from  the 
infilling  of  ancient  lake-basins  with  sediment,  in  the 
absence  of  direct  proof  of  the  fluviatile  origin  of 
the  alluvium,  and  it  may  be  suspected  that  many 
alluvial  tracts  which  have  been  asserted  to  occupy 
the  sites  of  ancient  lakes  are  really  the  result  of 
stream  action  only. 

Many  of  our  English  rivers  have  formed  fairly 
extensive  plains  where  they  traverse  soft  rocks ;  for 
example,  the  Yorkshire  Ouse,  where  it  flows  over 
the  Triassic  strata  of  the  Vale  of  York,  the  Great 


234    SCIENTIFIC   STUDY   OF   SCENERY 

Ouse,  in  its  course  over  the  Jurassic  clays  of  the 
neighbourhood  of  Bedford,  and  the  English  Dee, 
which  also  traverses  the  Triassic  rocks  in  the  lower 
part  of  its  course. 

In  the  case  of  the  large  rivers  of  the  continents, 
these  river-plains  are  often  very  extensive,  and  form 
important  features  in  the  scenery  of  a  continent.  I 
will  mention  one  example,  that  of  the  plain  of  the 
Mississippi,  which  has  a  length  of  over  600  miles 
in  a  straight  line  from  its  commencement  above  the 
junction  of  the  Ohio  to  its  termination  at  the  river's 
mouth.  Leaving  the  delta  out  of  account,  the  plain 
above  the  head  of  the  delta  has  a  width  of  eighty 
miles  at  the  mouth  of  the  White  river,  and  it  varies 
between  this  and  a  minimum  width  of  about  thirty 
miles. 

A  feature  may  be  noticed  in  this  place,  which  is 
often  of  considerable  importance  in  affecting  the 
scenery  of  a  river  valley,  namely,  the  existence  of 
river-terraces  upon  the  sides  of  the  valley.  If  a  river 
after  producing  an  alluvial  plain  is  subsequently 
enabled  to  corrade  vertically,  it  deepens  its  valley, 
and  the  sides  of  the  old  alluvial  plains  are  often 
left  above  the  present  river  level  as  terraces.  These 
terraces  may  be  formed  more  than  once,  and  we 
frequently  see  two  or  three  terraces  running  along 
the  sides  of  the  valley,  and  generally  parallel  to  the 
course  of  the  stream.  They  usually  have  a  flat 
upper  surface  (that  of  the  old  alluvial  plain  of  which 
they  were  portions),  and  may  slope  down  somewhat 
steeply.  As  they  are  generally  composed  of  porous 
materials,  and  give  a  dry  foundation  and  often  a 
copious  water  supply,  early  settlements  were  fre- 
quently situated  upon  these  terraces ;  for  instance, 


PLAINS   AND   PLATEAUX  235 

some  of  the  older  parts  of  London  are  situated  on 
the  gravel  terraces  which  there  border  the  river 
Thames. 

The  mode  of  infilling  of  lakes  by  sediment  and 
their  ultimate  conversion  into  plains  has  been  con- 
sidered in  Chapter  XII.  Scores  of  such  plains  often 
mark  the  sites  of  former  lakes  in  many  regions,  and 
a  lake  district  often  possesses  lakes  which  are  only 
a  small  percentage  of  those  which,  once  existent, 
have  been  destroyed  by  infilling  of  their  basins.  It 
has  been  remarked  above  that  there  is  considerable 
resemblance  between  these  infilled  lakes  and  the 
alluvial  flats  of  certain  reaches  of  rivers ;  the  former, 
however,  are  more  often  marked  by  a  covering  of 
peat-moss  over  the  sedimentary  deposits  than  are 
the  latter,  for  the  shallow  waters  of  the  margin  of 
a  partially  filled  up  lake  favour  the  growth  of 
vegetation,  which  rapidly  gives  rise  to  a  layer 
of  soil  rich  in  humus,  in  which  vegetation  continues 
to  flourish.  Turbaries  or  peat-mosses  marking  the 
sides  of  filled-in  lakes  are  frequently  encountered 
in  the  upland  regions  of%our  hilly  districts,  and  when 
surrounded  by  frowning  crags  produce  a  peculiar 
effect  upon  the  scenery,  especially  if  the  lake  be 
not  completely  filled  in,  when  a  pool  or  pools  of  dark 
brown  water  may  be  seen,  often  brightened  by  the 
blossoms  of  many  a  water-loving  plant,  as  the  water- 
lily  and  bog-bean,  or  the  pale  blue  flowers  on  the 
raceme  of  the  water-lobelia. 

Let  us  now  proceed  to  the  consideration  of  those 
plains  which  are  formed  by  the  accumulation  of 
sediment  in  the  sea,  and  the  ultimate  conversion  of 
the  tract  which  receives  this  sediment  into  land,  and 
we  may  first  deal  with  the  river-delta. 


236    SCIENTIFIC   STUDY   OF   SCENERY 

The  primary  cause  of  the  formation  of  a  delta, 
whether  in  a  lake  or  in  the  sea^  is  the  check  received 
by  the  river  current  when  it  enters  the  larger  body 
of  water.  It  has  been  seen  that  the  transporting 
power  of  a  current,  other  things  being  equal,  is 
dependent  upon  its  velocity,  and  as  the  velocity  is 
suddenly  diminished  when  the  river  enters  com- 
paratively still  water,  the  transported  sediment  is 
deposited.  In  the  case  of  the  sea,  should  a  marine 
current  of  sufficient  velocity  to  carry  away  the 
material  transported  by  the  river  sweep  past  the 
river's  mouth,  the  formation  of  a  delta  will  be  pre- 
vented ;  or  should  such  a  current  exert  its  influence 
subsequently  to  the  formation  of  a  delta,  the  further 
growth  of  that  delta  will  be  stopped,  as  has  hap- 
pened with  the  delta  of  the  river  Nile.  When  the 
river  enters  a  narrow  arm  of  the  sea,  as  a  fjord,  the 
shape  of  the  deltaic  tract  of  land  will  be  determined 
by  the  boundary  walls  of  the  fjord  ;  and  we  may  get 
tortuous  and  even  branched  strips  of  flat  land 
surrounded  by  comparatively  high  ground,  which 
originally  formed  the  sides -of  the  fjords,  as  seen, 
for  example,  in  the  case  of  the  ancient  fjords  of 
Carentan,  in  France,  and  those  near  Christiansand,  in 
Norway.1  As  a  general  rule,  the  widening  estuary 
of  a  river  becomes  filled  up,  and  then  the  delta 
grows  out  with  a  convex  front  to  the  open  water, 
giving  the  familiar  A  -shaped  form,  in  which  the  base 
of  the  A  possesses  the  convex  curve.  The  reason 
for  the  convex  curve  is  as  follows :  The  river  de- 
posits material  on  its  floor,  and  during  flood  seasons 
on  its  banks,  and  accordingly  the  level  of  the  river- 

1  For  figures  of  these  see   RECLUS'   The  Ocean,   English  edition, 
Figs.  54  and  55. 


PLAINS   AND   PLATEAUX  237 

bed  becomes  raised,  until  it  breaks  through  its  banks 
and  seeks  a  new  course,  when  the  same  thing  occurs. 
Accordingly,  in  time,  every  part  of  the  delta  is 
drained  by  the  river,  though  the  tendency  of  the 
stream  to  keep  its  initial  direction  causes  the 
greatest  amount  of  sediment  to  be  deposited  at  the 
point  situated  along  the  line  of  the  general  course 
of  the  river,  and  there  is  less  and  less  tendency  for 
deposition  to  occur,  as  one  passes  away  from  this 
point  on  either  side,  the  ideal  resultant  form  being 
that  of  the  arc  of  a  circle.  There  is  a  general, 
though  gentle,  slope  of  the  delta  above  the  surface 
of  the  water,  and  a  more  abrupt  sigmoidal  slope 
below  water,  which  will  only  affect  the  scenery  in  the 
case  of  deltas  which  have  been  laid  bare.  In  many 
cases  the  actual  outline  of  the  delta  is  far  more 
irregular  than  that  of  the  ideal  delta.  The  sides  of 
the  river  current  after  it  has  entered  the  sea  are  not 
so  swift  as  the  centre,  and  accordingly  deposition 
occurs  more  extensively  at  the  sides,  and  two  banks 
of  deposit  may  actually  be  raised  out  of  the  water 
with  the  current  flowing  between  them.  When  the 
river  has  deserted  this  channel,  the  channel  itself 
will  be  silted  up,  and  thus  finger-shaped  prolonga- 
tions may  extend  into  the  sea  beyond  the  general 
terminations  of  the  delta.  Such  finger-like  exten- 
sions are  seen  upon  the  delta  of  the  Mississippi. 

The  diversion  of  streams  is  due  not  only  to  over- 
flowing of  banks  during  floods,  but  to  obstruction 
by  sunken  timber  or  "  snags,"  or  even  by  extensive 
rafts  of  drift  timber,  which  block  the  channels  and 
cause  accumulation  of  sediment  against  the  upper 
sides.  Hence  we  frequently  find  an  intricate  rami- 
fication of  the  streams  of  deltas  well  shown  in  the 


238     SCIENTIFIC   STUDY   OF   SCENERY 

compound  delta  of  the  Ganges  and  Brahmaputra. 
In  the  low-lying  ground  of  the  deltas  marshy  con- 
ditions often  prevail,  and  accordingly  an  abundant 
growth  of  marsh  vegetation  usually  characterises 
deltaic  plains,  the  particular  character  of  the  vege- 
tation depending  upon  the  locality  of  the  delta,  and 
being  largely  dependent  upon  climatic  conditions. 
The  deltaic  deposits  of  Greenland,  due  to  the  de- 
position of  glacier  mud  at  the  heads  of  the  fjords, 
are  often  devoid  of  vegetation,  while  parts  of  the 
delta  of  the  Ganges  are  "overrun  with  reeds,  long 
grass,  the  Tamarix  Indica,  and  other  shrubs,  forming 
impenetrable  thickets,  where  the  tiger,  the  rhinoceros, 
the  buffalo,  deer,  and  other  wild  animals  take  shelter."1 

The  formation  of  lake  deltas  has  already  been 
considered  ;  they  differ  in  no  essential  particular  from 
those  formed  along  coast-lines,  the  main  difference 
being  due  to  the  absence  of  effective  tidal  action  in 
lakes,  which  affects  the  slopes  of  the  subaqueous 
portion  of  the  delta. 

In  many  regions,  where  numerous  rivers  reach  the 
sea  along  a  limited  tract  of  coast,  we  find  a  number 
of  coalescent  deltas  giving  rise  to  extensive  tracts 
of  new  land,  as,  for  instance,  along  the  north-west 
shores  of  the  Adriatic.  "  Here,"  states  Lyell,  "  from 
the  northern  part  of  the  gulf  of  Trieste,  where  the 
Isonzo  enters,  down  to  the  south  of  Ravenna,  there 
is  an  uninterrupted  series  of  recent  accessions  of 
land  more  than  100  miles  in  length,  which  within 
the  last  2000  years  has  increased  from  two  to  twenty 
miles  in  breadtli"  The  same  writer  notes  that  "Adria 
was  a  seaport  in  the  time  of  Augustus,  and  had,  in 

1  LYELL,  Sir.  C.,  Principles  of  Geology,  Eleventh  Edition,  vol.  i., 
chap.  xix. 


PLAINS   AND   PLATEAUX  239 

ancient  times,  given  its  name  to  the  gulf;  it  is  now 
about  twenty  Italian  miles  inland.  Ravenna  was 
also  a  seaport,  and  is  now  about  four  miles  from 
the  main  sea."  l  It  is  true  that  the  rate  of  growth 
of  this  deltaic  strip  has  increased  since  artificial 
banking  of  the  lower  portions  of  the  river  was 
resorted  to,  but  it  took  place  with  considerable 
rapidity  before  this.  The  area  of  the  great  plain 
of  Northern  Europe  is  being  gradually  increased 
by  the  silting  up  of  the  sea  margins  by  the  detritus 
brought  down  by  the  rivers  in  that  region. 

Another  method  of  formation  of  flat  land  by 
silting  up  of  an  area  originally  occupied  by  the 
sea,  is  owing  to  the  deposit  of  sea-silt,  which  has 
not  been  brought  down  by  the  rivers  of  the  neigh- 
bourhood, but  borne  from  a  distance.  The  English 
fenlands  supply  a  good  instance  of  a  plain  surface 
produced  in  this  manner.  Their  origin  has  been 
discussed  by  Mr.  S.  B.  J.  Skertchly  in  the  Geological 
Survey  Memoir,  treating  of  the  district,  and  also  in 
a  work  entitled  The  Fenland  by  that  author  and 
Mr.  S.  H.  Miller.  Skertchly  shows  that  the  fenland 
forms  a  portion  of  a  bay  which  has  been  silted  up, 
the  remaining  part,  the  Wash,  being  still  occupied 
by  the  sea,  and  the  silt  which  has  converted  the 
former  bay  into  land  is  not  mud  brought  down  by 
the  rivers  of  the  district,  but  marine  mud,  largely 
due  to  the  wash  of  the  Lincolnshire  and  Yorkshire 
coasts,  carried  into  the  bay  by  the  southward-moving 
tides.  The  process  of  silting  is  still  proceeding  at 
the  south  end  of  the  Wash,  but  further  south  the 
silt  dovetails  into  the  peat,  which  is  due  to  vegetable 

1  LYELL,  Sir  C.,  Principles  of  Geology,  Eleventh  Edition,  vol.  i., 
chap,  xviii. 


240     SCIENTIFIC   STUDY   OF   SCENERY 

growth,  and  there  is  no  doubt  that  peat  has  been 
formed  in  some  parts  contemporaneously  with  silt 
deposits  in  others.  That  earth-movement  has  par- 
ticipated in  the  formation  of  the  fens  is  shown  by 
the  occurrence  of  buried  forests  below  present  tide- 
level,  but  these  movements  are  merely  accessory,  and 
the  deposit  of  silt  and  growth  of  peat  upon  it  are 
the  essential  factors  in  fen-formation.  When  the  silt 
has  been  raised  to  a  height  of  about  eight  feet  above 
mean  tide-level  the  glasswort  (Salicornia  herbaced) 
begins  to  grow,  and  is  only  dry  towards  high  water. 
This  glasswort,  by  checking  the  flow  of  the  water, 
assists  in  the  deposition  of  the  silt.  When  the  flat 
has  increased  to  a  height  of  about  eleven  feet  above 
mean  tide-level  it  becomes  covered  with  verdure,  due 
to  plants  of  more  terrestrial  habit.1 

The  actual  peat  is  largely  due  to  marsh  vegetation, 
and  Skertchly  gives  reasons  for  supposing  that  the 
forest  growths  which  intervened  at  intervals  occurred 
during  periods  unfavourable  for  the  accumulation  of 
peat.2  The  peat  is  not  formed  of  Sphagnum,  like 
that  of  bogs,  but  consists  chiefly  of  the  decomposed 
remains  of  various  aquatic  herbaceous  plants."2 

According  to  Skertchly  the  peat  in  some  places 
is  entirely  made  up  of  Hypnum  fluitans.  Other 
plants  which  contribute  to  it  are  various  rushes  and 
sedges,  including  Cladium  mariscus,  also  the  bladder- 
wort,  starwort,  and  arrowhead,  while,  in  the  shallow 
waters  of  the  meres,  a  calcareous  marl  was  formed 
by  the  growth  of  Chara. 

The  beauty  of  the  fenland  is  the  result  of  the 
atmospheric  conditions  and  the  nature  of  the  vegeta- 

1  See  The  Fenland,  p.  223. 

1  BABINGTON,  C.  C,  Flora  of  Cambridgeshire,  p.  xviii. 


PLAINS   AND   PLATEAUX  241 

tion.  The  glorious  sunrises  and  sunsets,  and  the 
magnificence  of  the  cloud  effects  have  frequently 
been  described.  The  peculiar  vegetation  of  the 
fenland  has  nearly  disappeared,  though  the  flora 
which  once  occupied  the  meres  still  brightens  the 
ponds  and  dikes  which  are  scattered  through  the 
cultivated  tracts,  and  one  piece  of  undrained  fen, 
Wicken  Fen,  yet  survives  to  show  the  nature  of 
the  former  uncultivated  plain.  There  one  can  still 
roam  through  the  sedges  and  rushes,  and  observe  the 
fronds  of  the  mar«h  fern  (Lastr&a  thelypteris]  and 
the  blossoms  of  many  a  fenland  plant.  The  great 
pit  at  Roslyn,  near  Ely,  filled  with  water  at  the 
bottom,  gives  some  notion  of  the  former  appear- 
ance of  the  fenland  meres.  Anyone  looking  over  the 
open  spaces  between  the  reeds  from  a  boat,  when  the 
banks  are  out  of  sight  and  the  water  is  covered  in 
one  place  with  the  leaves  and  flowers  of  the  yellow 
and  white  water  lilies,  in  another  with  the  pale 
yellow  flowers  of  the  bladderwort,  and  yet  again 
with  the  beautiful  yellow  blossoms  of  the  Limnan- 
themum,  can  well  imagine  that  he  is  afloat  on  one  of 
the  meres  of  the  pristine  fenland,  and  the  knowledge 
that  the  flat  places  of  the  earth  may  be  filled  with 
beauty  is  here  brought  home  to  one  in  a  striking 
manner. 

Marine  deposits  may  give  rise  to  plains  as  the 
result  of  uplift,  and  these  plains  will  not  differ 
markedly  from  those  formed  by  silting  up  of 
former  sea-tracts,  except  that  in  all  probability  the 
seaward  slope  will  be  somewhat  greater.  The  coastal 
plain  of  the  east  coast  of  North  America  is  of  this 
nature,  and  it  serves  as  a  good  example  of  this  class 
of  plain. 


242     SCIENTIFIC   STUDY   OF   SCENERY 

The  last  plains  to  be  considered  are  those  which 
are  termed  plains  of  marine  denudation.  Their 
mode  of  production  will  be  more  fully  considered 
when  we  discuss  the  operations  of  the  sea  at 
length.  It  will  be  sufficient  here  to  remark  that 
the  erosive  power  of  the  sea  is  limited  to  the 
superficial  portion  which  is  affected  by  waves 
and  currents,  and  as  the  depth  to  which  these 
operate  is  practically  the  same  in  all  places,  the 
ultimate  result  of  marine  denudation  is  to  give  rise 
to  a  comparatively  level  surface  coinciding  with  the 
downward  limit  of  operation  of  the  waves  and 
currents.  This,  if  uplifted,  will  be  a  plain  of  marine 
denudation,  and  it  will  differ  from  a  peneplain  mainly 
in  the  absence  of  weathered  material  upon  its  surface, 
whereas  the  peneplain  will  usually  retain  some  of 
the  products  of  weathering  upon  the  rocks  which 
underlie  it. 

The  amount  of  the  surface  of  the  land  which  is 
of  the  nature  of  plain  is  very  great.  A  great  tract 
of  plain  extends  from  the  western  shores  of  Europe 
to  the  Altai  Mountains  in  Asia,  unbroken  save  by 
the  Ural  Mountains,  and  covering  an  area  approach- 
ing 5,000,000  square  miles,  or  nearly  one-third  of  the 
Eurasian  continent.  As  plains  usually  yield  a  soil 
which  is  pre-eminently  cultivable,  it  is  found  that 
the  population  is  extensively  gathered  upon  the 
plains,  and  much  of  their  surface  is  actually  under 
cultivation.  When  uncultivated  the  scenery  of  a 
plain  depends  largely  on  the  nature  of  the  vegeta- 
tion. We  find  one  plain  differing  considerably  over 
different  portions  of  its  surface,  owing  to  change  in 
vegetation,  and  the  names  which  are  given  to  plains 
are  often  determined  to  some  extent  by  the  character 


PLAINS    AND   PLATEAUX  243 

of  the  prevalent  vegetation.  The  rolling  grass- 
covered  plains  of  North  America  are  prairies,  and 
in  some  places  savannahs ;  the  river  plains  of  South 
America,  overflowed  during  the  rainy  season  and 
covered  with  grass,  but  dry  during  the  periods  of 
drought,  are  called  llanos  ;  in  the  same  country  the 
forest-clad  plains  are  known  as  selvas,  as  in  the 
basin  of  the  Amazon  ;  the  thistly  and  grassy  plains 
of  Parana  and  La  Plata,  alternating  with  bogs  and 
often  parched  during  the  season  of  drought,  are 
pampas;  in  the  Old  World  the  belt  of  jungle  between 
Hindustan  and  the  Himalayas,  due  to  the  detritus 
brought  down  by  the  Himalayan  rivers,  is  called 
tarai ;  the  boggy  flats  of  Siberia  are  tundras.  The 
tundras  and  pampas  approach  the  condition  of 
deserts ;  the  amount  of  vegetation  is  in  parts  very 
sparse,  and  there  is  a  gradual  passage  into  deserts. 

The  same  plain  may  present  different  aspects  in 
different  parts.  Thus  the  great  plain  of  Europe  and 
Siberia  is  cultivated  river  plain  (polders)  in  one  place, 
sandy  heath  in  another,  wooded  flats  in  a  third,  and 
desert  in  a  fourth.  The  most  luxuriant  vegetation 
occurs  on  the  plains  in  temperate  regions,  and  in 
sub-tropical  regions  supplied  with  abundant  rain ; 
in  sub-tropical  regions  of  drought,  the  amount  of 
vegetation  rapidly  declines,  and  the  same  is  the  case 
in  Arctic  regions.  In  the  latter  the  vegetation  be- 
comes stunted,  and  we  find  plains  occupied  by  copses 
of  dwarf  willows  and  birches  rarely  rising  to  a  man's 
height,  or  by  grasses,  mosses,  and  lichens,  intermixed 
with  brightly  flowering  plants,  oftpn  in  cushion- 
shaped  masses. 

Plateaux. — The  elevated  tracts  of  country  known 
as  plateaux  may  be  due  to  (i)  accumulation,  (2) 


244     SCIENTIFIC   STUDY   OF   SCENERY 

elevation  of  a  pre-existing  low-lying  flat  tract,  or 
(3)  denudation  of  an  elevated  region  to  one  level. 

The  principal  plateaux  of  accumulation  are  due 
to  the  outflow  of  very  liquid  lavas  which  accumulate 
over  one  another  in  a  series  of  sheets,  each  approach- 
ing to  a  condition  of  perfect  horizontality.  The 
great  lava  flows  of  the  Deccan,  in  India,  have  pro- 
duced a  plateau  of  this  character.  The  lava  flows 
of  the  Deccan,  according  to  Messrs.  Medlicott  and 
Blanford,  have  a  thickness  of  about  6000  feet,  and 
occupy  an  area  of  about  200,000  square  miles,  giving 
rise  to  plateaux  of  remarkable  horizontality.  Similar 
plateaux  are  found  among  the  Western  Territories 
of  North  America,  as,  for  instance,  in  Idaho.  As 
the  mode  of  origin  of  these  lavas  has  already  been 
discussed,  we  need  say  no  more  concerning  lava- 
formed  plateaux. 

Typical  plateaux  formed  by  uplift  are  also  found 
among  the  slightly  disturbed  rocks  of  the  North- 
western Territories.  The  rocks  of  this  region  are 
usually  slightly  inclined  over  wide  areas,  but  broken 
up  into  blocks  by  faults,  or  uplifted  by  the  existence 
of  hogbacks,  and  accordingly  we  find  plateaux  "  with 
broken  edges  where  they  are  bounded  by  faults, 
flexed  edges  where  they  are  bounded  by  monoclinal 
flexures,  and  escarpments  where  they  are  bounded 
by  canons  or  lines  of  cliffs."1  Powell  figures  a 
series  of  plateaux  north  of  the  Grand  Canon  of 
the  Colorado.  Of  these,  the  most  westerly,  Shi- wits 
plateau,  is  bounded  on  the  west  by  a  canon,  on  the 
east  by  a  fault ;  the  central  one,  the  Kanab  plateau, 
is  faulted  on  the  west,  and  cut  through  by  a  canon  in 
the  centre,  and  above  it  rises  the  Kaibab  plateau, 
1  POWELL,  J.  W.,  Geology  of  the  Mista  Mountains,  p.  14. 


PLAINS   AND   PLATEAUX  245 

bounded  on  either  side  by  a  hogback  or  monoclinal 
fold.  In  Figure  5  he  gives  a  bird's-eye  view  of  a 
part  of  the  Musinia  zone  of  displacement,  where 
a  tract  of  country  is  broken  up  into  horizontal  or 
slightly  sloping  plateaux,  each  formed  by  a  fractured 
mass  of  the  earth's  crust,  bounded  by  faults  on  all 
sides. 

Many  of  the  great  plateaux  of  the  world,  as  that 
of  Central  Asia,  are  also  due  to  uplift,  though  no 
doubt  modified  by  denudation.  In  the  case  of  these 
plateaux  the  scale  is  so  large  that  considerable 
differences  of  level  do  not  destroy  the  plateau-like 
character  of  the  whole.  We  may  find  them  cut  up 
by  deep  valleys,  and  traversed  by  extensive  mountain 
chains,  and  yet  the  plateau-structure  can  be  discerned 
through  these  minor  complications. 

The  uplifted  area  may  be  one  which  originally 
possessed  horizontality  before  its  uplift,  owing  to 
the  accumulation  of  sediment,  the  formation  of  a 
peneplain  by  subaerial  denudation,  or  the  formation 
of  a  plain  of  marine  denudation  owing  to  the  action 
of  the  sea.  In  each  case,  if  the  upward  movement 
is  one  of  sufficient  extent  to  preserve  a  general 
horizontality  of  the  upraised  block  of  earth's  crust,  a 
plateau  will  result. 

In  the  case  of  plateaux  formed  by  denudation,  as 
in  those  due  to  accumulation  and  the  greater  number 
of  those  originating  in  an  uplift,  general  horizontality 
of  the  strata  is  a  necessary  condition  for  the  pro- 
duction of  the  plateaux;  and  one  .need  hardly  observe 
that  uplift  must  precede  or  accompany  denudation 
in  order  that  the  strata  may  reach  the  required 
height.  Indeed,  with  plateaux,  as  with  mountains, 
though  we  can  separate  those  due  to  uplift  from 


246     SCIENTIFIC   STUDY   OF   SCENERY 

those  due  to  denudation,  the  two  processes  must 
always  take  place  ;  and  a  plateau  will  be  placed  in 
one  or  the  other  class,  according  as  its  salient 
features  are  primarily  produced  by  uplift  or  by 
denudation. 

Plateaux  due  to  denudation  are  specially  prone  to 
occur  when  a  comparatively  level  plane  of  demarca- 
tion separates  overlying  rocks,  which  are  easily 
denuded,  from  underlying  ones  which  resist  denuda- 
tion. They  very  frequently  occur  on  the  upper 
surfaces  of  limestone  strata,  which  were  succeeded 
by  ordinary  mechanical  sediments.  It  has  already 
been  shown  that  limestones  largely  resist  subaerial 
denudation,  owing  to  the  absence  of  surface  drainage, 
and  accordingly,  while  overlying  mechanical  sedi- 
ments are  cleared  away  by  this  kind  of  denudation, 
the  limestone  is  left  practically  intact,  except  as 
regards  minor  changes.  A  considerable  plateau  of 
limestone,  cut  up  by  the  valleys  of  the  Ribble,  Dale 
Beck,  and  some  minor  streams,  ends  in  the  neighbour- 
hood of  Settle,  in  Yorkshire.  Some  of  the  overlying 
mechanical  sediments  have  not  yet  been  destroyed, 
and  stand  up  above  the  general  limestone  plateau, 
forming  the  summits  of  Whernside,  Ingleborough, 
and  Penyghent ;  and  from  the  top  of  any  of  these 
hills  the  regularity  of  the  limestone  plateau  may  be 
noted.  The  peculiar  effect  of  weathering  along  joints, 
giving  rise  to  "  clints,"  has  already  been  described  in 
Chapter  VIII.  These  clints  are  specially  well  shown 
on  the  plateau  of  the  Settle  district. 

Plateaux  of  denudation  occurring  on  a  larger  scale 
are  often  irregular  and  present  many  inequalities. 

Owing  to  the  elevation  of  plateaux  they  are  liable 
to  be  carved  out  by  denudation  to  a  greater  extent 


PLAINS   AND   PLATEAUX  247 

than  plains ;  and  as  the  strata  of  a  plateau-region  so 
often  approach  horizontally,  the  hills  which  are 
formed  from  a  plateau  by  erosion  are  apt  to  be 
tabular  and  flat-topped.  Before  the  hill  stage  is 
reached  the  plateau  may  be  cut  up  by  deep  narrow 
valleys,  as  in  the  case  of  the  Colorado  Region 
of  North  America.  These  valleys  are  often  invisible 
until  the  traveller  reaches  their  brinks ;  and  accord- 
ingly the  aspect  of  the  plateau  is  that  of  a  horizontal 
tract  of  country,  though  that  country  may  be  actually 
carved  out  to  a  considerable  degree  by  the  rivers 
which  traverse  it. 

As  the  valleys  widen,  the  intervening  tabular  hills, 
or  mesas  as  they  are  termed  in  some  parts  of 
America,  become  more  and  more  pronounced,  and 
small  isolated  "  outliers "  standing  away  from  the 
main  cliff  form  "  buttes." 

The  ultimate  result  of  subaerial  denudation  acting 
upon  a  plateau,  as  upon  a  mountain  district,  will 
be  to  reduce  it  to  a  peneplain. 


CHAPTER  XV. 
DESERTS 

THE  effect  of  climate  has  been  incidentally 
mentioned  more  than  once  in  the  preceding 
chapters,  but  we  must  now  take  into  account  the 
influence  of  abnormal  conditions  of  climate  in 
affecting  the  scenery  of  certain  regions  of  the  earth. 
The  principal  conditions  to  which  we  must  now  pay 
attention  are  those  of  exceptional  drought  and  of 
exceptional  cold,  and  it  is  to  the  former  that  we 
owe  the  existence  of  deserts,  while  to  the  latter  are 
due  certain  features  which  will  be  described  in 
subsequent  chapters. 

No  area  of  the  earth's  surface  is  absolutely  free 
from  precipitation  of  the  aqueous  vapour  which  is 
held  in  the  atmosphere,  in  the  form  of  either  rain 
or  snow,  and  desert  regions  are  merely  due  to  paucity 
of  rainfall  and  not  to  its  actual  non-occurrence.  As 
any  inequality  in  the  earth's  surface  causes  vapour- 
laden  atmosphere  to  rise  and  become  chilled,  and 
thereby  renders  it  incapable  of  retaining  so  much 
moisture  as  it  could  hold  at  a  lower  level,  upland 
regions  are  apt  to  be  favoured  with  much  rain,  and 
lowland  regions  are  often  comparatively  dry.  Hence, 
other  things  being  equal,  desert  conditions  are  more 
liable  to  be  developed  in  plains  than  in  districts 
marked  by  great  inequalities  of  surface,  and 
248 


DESERTS  249 

geographers  have  frequently  treated  of  plains  and 
deserts  as  though  they  were  very  intimately 
associated.  But  a  district  may  be  very  uneven, 
and  if  all  the  winds  which  blow  over  that  district 
carry  air  charged  with  very  little  aqueous  vapour, 
that  vapour  need  not  be  deposited,  even  when  the 
ground  rises  to  considerable  elevations.  Deserts, 
then,  though  often  coincident  with  plains,  are  also 
frequently  found  in  hilly  regions,  though  even  then 
some  of  the  processes  which  occur  in  desert  regions, 
which  will  be  immediately  described,  tend  to  level 
pre-existing  inequalities. 

Leaving  out  of  account  those  barren  regions  which 
owe  their  barrenness  to  the  condensation  of  vapour 
as  snow  and  not  as  rain,  we  shall  find  that  deserts 
occur  most  frequently  in  sub -tropical  regions.  In 
most  tropical  regions  the  rainfall  during  the  rainy 
season  is  excessive,  and  we  require  something  besides 
great  heat  for  the  existence  of  ordinary  deserts, 
something  which  greatly  reduces  the  annual  rainfall, 
and  produces  long  periods  of  drought.  The  con- 
ditions favourable  for  the  existence  of  deserts  on  a 
large  scale  occur  when  an  extensive  mountain  range 
separates  a  large  tract  of  continent  from  the  pre- 
vailing vapour-laden  winds  blowing  from  the  ocean, 
and  these  conditions  are  fulfilled  in  all  our  great 
desert-regions.  The  vapour-laden  winds  strike  the 
seaward  side  of  the  mountains,  are  compelled  to 
rise,  become  chilled,  and  deposit  a  large  quantity 
of  their  aqueous  vapour.  They  reach  the  lee  side 
of  the  mountains  robbed  of  most  of  their  moisture, 
and  as  they  then  pass  from  higher  to  lower  levels 
they  are  able,  when  reaching  the  lowlands,  to  hold 
much  more  moisture  than  they  actually  possess,  and 


250     SCIENTIFIC   STUDY   OF   SCENERY 

accordingly  the  rainfall  is  exceedingly  limited.  The 
desert  of  Gobi  in  Asia  is  practically  surrounded  by 
mountains,  which  drain  the  winds  of  their  contained 
moisture.  The  great  Sahara  Desert,  occupying  an 
area  about  two-thirds  of  that  of  Europe,  is  also  shut 
off  from  the  prevailing  winds  which  cross  expanses 
of  ocean  by  mountain  ranges,  as  is  likewise  the 
Kalahari  Desert  of  South  Africa.  In  North  America 
a  desert  region  in  the  North-west  Territories  is  prac- 
tically surrounded  by  mountains ;  in  South  America 
a  desert  region  exists  in  Chili  and  Peru  to  the  west 
of  the  Andes,  for  the  moisture-laden  winds  there 
blow  from  the  east.  In  Central  Australia,  again,  we 
have  a  desert  tract  separated  from  the  sea  by 
elevated  land. 

An  examination  of  a  map  of  existing  deserts 
shows  that  they  are  chiefly  confined  to  a  belt  of 
country  lying  between  20°  and  45°  on  either  side  of 
the  equator,  that  is  between  the  belt  of  tropical 
rains  and  the  regions  of  cold,  and  it  is  evident 
from  this  distribution  that,  apart  from  local  causes, 
the  deserts  owe  their  existence  to  general  meteor- 
ological conditions.  Should  these  conditions  alter, 
the  distribution  of  deserts  will  be  affected.  At  the 
present  day  we  have  our  desert-belts  as  well  defined 
as  our  glacial  regions,  but  just  as  in  past  times 
glaciation  has  affected  areas  which  now  enjoy  a 
genial  climate,  similar  areas  have  formerly  been 
marked  by  desert  conditions.  In  the  northern  belt 
of  deserts  we  find  the  desert  area  of  Central  Asia, 
and  that  stretching  from  the  west  coast  of  Africa 
into  Arabia  and  Persia,  and  in  the  New  World  the 
desert  regions  of  the  western  territories  of  North 
America.  In  the  southern  belt  lie  the  Australian 


DESERTS  251 

desert,  the  Kalahari  desert  of  Africa,  and  the  South 
American  desert  tracts. 

The  scenery  of  deserts,  as  of  other  areas,  is  largely 
determined  by  the  agents  of  erosion  and  accumula- 
tion, but  the  characteristic  features  are  due  to  the 
particular  character  of  these  agents  in  the  desert 
regions.  There  are  four  different  kinds  of  deserts, 
namely  rock-deserts,  gravel-deserts,  sand-deserts,  and 
loam -deserts.  In  the  rock-deserts  the  agents  of 
transportation  are  sufficiently  powerful  to  remove 
the  results  of  disintegration  of  the  rocks,  leaving  a 
surface  of  bare  rock  ;  in  the  others  the  disintegrated 
material  remains  over  the  spot  where  disintegration 
has  occurred,  or  it  has  been  accumulated  by  transport 
from  other  regions,  and  the  latter  action  is  the  cause 
of  the  more  important  desert  tracts  being  covered  by 
loose  accumulations,  for  it  is  rare  to  find  the  material 
remaining  on  the  spot  where  it  is  disintegrated. 

If  a  desert  region  has  acquired  its  present  characters 
in  geologically  recent  times,  the  present  agents  in 
operation  in  that  region  may  not  have  been  able  to 
efface  the  features  produced  when  other  conditions 
prevailed,  and  it  is  of  importance  to  determine  how 
long  an  existing  desert  has  possessed  its  present 
conditions.  This  is  not  always  an  easy  matter  to 
decide,  but  there  is  considerable  reason  for  supposing 
that  at  no  distant  period  the  rainfall  of  the  desert 
region  of  the  North-western  Territories  of  North 
America  was  greater  than  it  now  is,  while  recent 
research  points  to  the  prevalence  of  desert  conditions 
in  the  eastern  part  of  the  North  African  desert  tract 
through  long  periods  of  time. 

It  must  also  be  borne  in  mind  that  the  term  desert 
is  not  one  which  can  be  strictly  defined  ;  a  desert  is  a 


252     SCIENTIFIC   STUDY   OF   SCENERY 

region  where  the  rainfall  is  insufficient  to  allow  of 
the  growth  of  much  vegetation,  but  there  is  every 
gradation  from  a  desert  region  to  one  which  we 
are  apt  to  consider  as  one  which  possesses  normal 
characters,  and  the  amount  of  rainfall,  though  small 
in  all  deserts,  is  much  greater  in  some  than  in  others. 
Erosion  of  Deserts.  The  peculiar  character  of 
deserts  is  not  only  directly  dependent  upon  the 
scarcity  of  rain,  but  also  indirectly  by  its  influence 
upon  vegetation,  as  pointed  out  by  Gilbert  in  the 
following  passage1: — 

"Vegetation  favours  the  disintegration  of  rocks,  and 
retards  the  transportation  of  the  disintegrated  material. 
Where  vegetation  is  profuse  there  is  always  an  excess  of 
material  awaiting  transportation,  and  the  limit  to  the  rate  of 
erosion  comes  to  be  merely  the  limit  to  the  rate  of  trans- 
portation. And  since  the  diversities  of  rock  texture,  such 
as  hardness  and  softness,  affect  only  the  rate  of  disentegra- 
tion  (weathering  and  corrasion)  and  not  the  rate  of  trans- 
portation, these  diversities  do  not  affect  the  rate  of  erosion 
in  regions  of  profuse  vegetation,  and  do  not  produce 
corresponding  diversities  of  form. 

"  On  the  other  hand,  where  vegetation  is  scant  or  absent, 
transportation  and  corrasion  are  favoured,  while  weathering 
is  retarded.  There  is  no  accumulation  of  disentegrated 
material.2  The  rate  of  erosion  is  limited  by  the  rate  of 
weathering,  and  that  varies  with  the  diversity  of  rock 
texture.  The  soft  are  eaten  away  faster  than  the  hard,  and 
the  structure  is  embodied  in  the  topographic  forms. 

"Thus  a  moist  climate,  by  stimulating  vegetation,  pro- 
duces a  sculpture  independent  of  diversities  of  rock  texture, 
and  a  dry  climate  by  repressing  vegetation  produces  a 
sculpture  dependent  on  those  diversities." 

1  GILBERT,  G.  K.,   Geology  of  the  Henry  Mountains ;  p.  113. 

2  That  is,  over  the  spot  where  the  disintegration  occurs. 


DESERTS  253 

Owing  to  the  character  of  desert  climates  rain  and 
rivers  play  a  minor  part  in  the  determination  of 
desert  features,  and  the  main  work  of  destruction 
and  transport  is  due  to  changes  of  temperature 
acting  directly,  or  indirectly  in  the  form  of  wind. 
Disintegration  is  mainly  caused  by  change  of  tem- 
perature, as  already  noted  in  Chapter  VI4-,  though 
it  is  assisted  by  wind,  and  to  a  minor  degree  by 
chemical  weathering. 

The  changes  of  temperature  cause  the  fracture 
of  the  rock,  owing  to  its  alternate  expansion  and 
contraction.  Not  only  does  the  rock  mass  con- 
tract and  expand  as  a  whole,  but  it  is  known 
that  expansion  takes  place  in  a  crystal  in  different 
degrees  along  different  crystalline  axes,  and  this  no 
doubt  helps  the  fracture.  The  fracture  is  frequently 
assisted,  owing  to  the  presence  of  salts  in  the  rock. 
Many  rocks  in  desert  regions  were  formerly  de- 
posited in  the  sea,  and  contain  sea-salts,  which, 
owing  to  the  dry  conditions,  have  not  been  dissolved 
or  removed.  These  salts  come  to  the  surface,  owing 
to  capillary  action,  and  being  hygroscopic,  are  dry  in 
the  daytime  and  damp  at  night,  and  owing  to  the 
alternate  change  from  wet  to  dry  conditions,  the 
rocks  are  cracked  in  much  the  same  way  as  that  in 
which  they  are  cracked  by  frost  in  higher  latitudes.1 

Wind  transports  material,  and  produces  much  the 
same  results  in  nature  as  are  produced  artificially 
by  the  sand-blast.  Pebbles  are  gradually  worn 
down,  often  presenting  edges,  rocks  may  be  striated, 
and  pebbles  and  rocks  alike  often  have  a  polished 

1  See  WALTHER,  J.,  Denudation  in  der  Wuste,  Abhandl.  der 
math.-phys.  Classe  der  K.  Sachs  Gesellsch.  der  Wissenschaften,  bd. 
XVL,  Leipzig,  1891. 


254     SCIENTIFIC   STUDY   OF   SCENERY 

appearance,  as  the  result  of  the  sand-blast.  In  the 
gravel  desert  of  Morocco  Walther  describes  the  area 
as  presenting  a  general  varnished  appearance,  owing 
to  the  action  of  the  sand-blast  upon  the  little  pebbles 
with  which  the  desert  is  strewn. 

The  general  absence  of  running  water  on  the  hills 
of  desert  regions  is  indicated  by  the  absence  of  the 
characteristic  curve  of  water  erosion,  and  the  pro- 
duction of  house-roof  structure,  as  seen  in  the  picture 
of  the  Ras  Muhammed  desert  in  the  Sinaitic  Peninsula 
figured  in  Plate  III.  of  Walther's  paper  on  the  Coral 
Reefs  of  that  peninsula,  and  also  in  the  outlines  of 
the  hills  in  the  same  peninsula  figured  on  p.  389  of 
his  paper  on  the  "  Denudation  of  Deserts."  Another 
feature  of  desert  hills  is  the  absence  of  accumulation 
of  loose  material,  such  as  screes  and  rainwash  at  the 
foot  of  the  hills — the  action  of  the  wind  being 
sufficiently  powerful  to  remove  the  material.  The 
mountains  of  deserts,  therefore,  have  a  character  of 
their  own ;  they  differ  from  those  of  temperate 
regions  in  the  absence  of  the  curve  of  water  erosion, 
and,  although  resembling  those  of  Arctic  lands  in 
the  general  straightness  of  their  sides,  they  have 
not  the  accumulation  of  loose  material  so  fre- 
quently found  at  the  foot  of  the  hills  of  frost-bound 
regions. 

The  action  of  the  wind  removes  the  softer  rocks, 
leaving  the  harder  ones  behind,  as  noticed  by  Gilbert, 
and  also  enlarges  the  lines  of  weakness,  as  joints  and 
planes  of  stratification.  In  areas  composed  of  hori- 
zontal strata,  the  soft  rocks  are  removed,  and  the 
area  lowered  to  the  level  of  a  harder  stratum,  which 
gives  rise  to  a  level  plateau  ;  this  in  turn  gets  cut  up, 
and  the  whole  region  reduced  to  a  lower  level  coin- 


DESERTS  255 

cident  with  the  surface  of  the  next  hard  stratum, 
and  the  process  of  levelling  is  continued  in  the 
same  way.  One  result  of  this  weathering  is  to  pro- 
duce isolated  columns,  often  undercut  at  the  base, 
and  etched  into  different  shapes  by  the  wind  acting 
unequally  upon  rocks  of  different  hardness,  and 
accordingly  the  detailed  scenery  of  desert  uplands 
recalls  that  of  a  group  of  mountains  composed  of 
dolomite. 

The  effect  of  the  wind  on  a  rock  presenting  vary- 
ing degrees  of  hardness  is  well  seen  in  that  from 
which  the  sphinx  of  Gizeh  is  carved  out.  The 
lower  part  of  the  sphinx  has  been  affected  by  wind 
action,  and  as  different  parts  of  the  rock  differ  in 
hardness,  owing  to  the  infiltration  of  iron  compounds 
forming  ring-shaped  masses,  the  softer  parts  have 
been  etched  by  the  wind,  leaving  the  harder  parts 
outstanding  in  ring-shaped  bands. 

When  rounded,  hard  masses  occur  in  a  rock  on 
a  flat  surface,  they  not  only  stand  out  from  the 
surrounding  rock  owing  to  the  sand-blast,  but  a 
ridge  of  rock  which  is  protected  by  them  is  left  on 
the  lee  side,  as  shown  by  Walther  in  Fig.  55  of 
his  work  on  the  Denudation  of  Deserts,  where 
manganese  concretions  in  the  Nubian  sandstone  of 
the  Sinaitic  desert  have  caused  the  formation  of 
such  ridges. 

Certain  outlines  due  to  denudation  are  found  on  a 
small  scale  in  some  desert  regions,  which  present 
difficulties  with  regard  to  their  explanation.  The 
clayey  deposits  of  the  neighbourhood  of  the  Henry 
Mountains  in  the  Colorado  region,  and  the  old 
lacustrine  deposits  of  the  country  around  the  salt 
lakes  of  Utah  and  in  parts  of  Wyoming,  are  known 


256     SCIENTIFIC   STUDY   OF   SCENERY 

as  "  Bad  Lands."  "  This  expressive  name  has  been 
given  to  some  of  the  strangest  and,  in  many  respects, 
most  repulsive  scenery  in  the  world.  They  are 
tracts  of  irreclaimable  barrenness,  blasted  and  left  for 
ever  lifeless  and  hideous."'  Those  of  Wyoming  are 
carved  into  buttes  and  intervening  depressions  largely 
by  wind  action,  whereas  near  the  Henry  Mountains 
rain  has  caused  xthe  development  of  very  regular 
water-ways,  in  which  the  Thalwegs  present  the 
normal  curve  of  stream  denudation  at  the  base, 
whereas  the  summits  of  the  ridges  have  a  convex 
curve,  though  the  nature  of  the  rock  appears  to  be 
the  same  at  base  and  summit.  Gilbert  quotes  these 
Bad  Land  ridges  as  exceptions  from  the  ordinary 
law  of  water-erosion,  which  are  as  yet  unexplained. 

In  some  deserts,  like  that  of  Egypt,  the  flat  ground 
is  carved  out  into  butte-like  elevations  from  six  to 
ione  hundred  and  fifty  feet  in  height,  known  as 
"  Zeugen."  They  consist  of  soft  rock  with  a  layer  of 
hard  rock  at  the  summit,  and  beneath  the  hard  cap 
the  soft  rock  is  carved  into  slopes  which  resemble 
the  typical  denudation  curve,  as  shown  in  Fig.  36. 
Nevertheless,  according  to  Walther,  running  water 
plays  no  part  in  their  formation,  as  proved  among 
other  things  by  their  most  frequent  occurrence  in 
regions  of  least  rainfall.  He  accounts  for  them  on 
the  supposition  that  they  are  due  to  wind  action, 
assisted  by  chemical  weathering.  When  a  hollow 
has  once  been  formed  by  the  wind,  weathering  comes 
into  play  with  different  effectiveness  on  different 
parts  of  the  slope.  Immediately  below  the  hard  cap 
the  rock  retains  what  water  it  takes  up,  owing  to  the 
shade  of  the  overlying  hard  cap,  and  accordingly 

1  GEIKIE,  Sir  A.,  Geological  Sketches  at  Home  and  Abroad,  No.  ix. 


DESERTS  257 

chemical  weathering  is  most  pronounced  there,  and 
the  rock  is  rendered  less  coherent,  and  is  easily 
transported  by  the  wind;  below  this  the  cap  offers 
less  and  less  protection,  and  the  removal  of  the  rock 
occurs  in  smaller  and  smaller  quantity,  until  the 
curve  is  produced  and  the  hard  cap  overhangs.  As 
the  shady  side  of  the  Zeuge  is  weathered  to  a  greater 
extent  than  the  sunny  side,  the  Zeuge  becomes 
crooked  and  the  top  breaks  off,  when  all  the  soft 
material  is  removed,  and  the  process  is  commenced 


FIG.  36. 
Ideal  section  across  a  Zeuge. 

afresh  at  a  lower  level  with  another  soft  stratum 
surmounted  by  a  hard  one. 

According  to  Walther,  the  influence  of  shade 
causing  water  to  remain  in  shady  spots  longer  than 
elsewhere,  and  thereby  permitting  chemical  weather- 
ing to  occur  more  extensively  in  the  shade,  is  also 
responsible  for  the  formation  of  extensive  holes  on 
the  general  surface  of  a  rock  desert.  When  these 
holes  are  once  formed  the  shade  in  the  interior 
becomes  more  pronounced,  and  accordingly  the 
cavities  grow  wider  as  they  proceed  further  down 
beneath  the  general  surface  of  the  rock. 

The  fretted  nature  of  wind-worn  rocks  in  a  desert 
region  is  increased,  owing  to  the  production  of  a 
peculiar  brown  crust,  which  has  been  noticed  by 
many  writers,  e.g.  Messrs.  Brindley  and  Floyer, 
which  gives  a  sameness  of  colouring  to  many 


258     SCIENTIFIC   STUDY   OF   SCENERY 

deserts.  This  crust  has  generally  been  -  referred  to 
the  effects  of  weathering,  but  Walther  gives  reasons 
against  its  production  by  simple  weathering  action. 
It  consists  mainly  of  peroxides  of  iron  and  manga- 
nese, and  rocks,  like  limestone,  which  do  not  contain 
these  substances  are  covered  by  it,  equally  with 
those  rocks  which  do  contain  them. 

When  cliffs  of  rock  are  covered  with  the  brown 
crust,  it  scales  off  in  vertical  strips  in  some  un- 
explained manner,  possibly  owing  to  the  trickling  of 
rain-water.  The  exposed  parts  are  influenced  by 
the  denuding  action  of  desert  agents,  as  weathering 
in  the  shade  and  the  sand-blast,  while  the  encrusted 
parts  resist  this  action.  The  first  result  is  the  pro- 
duction of  window-like  recesses  in  the  exposed  parts. 
As  the  backs  of  these  recesses  are  in  the  shade,  the 
action  goes  on  sideways  behind  the  crust-protected 
intervening  parts,  producing  passages  behind  the 
protected  portions,  which  then  remain  as  pillars 
between  the  window-shaped  apertures.  Some  of 
these  apertures  are  large  enough  for  a  man  to  enter 
in  a  stooping  position. 

Again,  when  the  upper  part  of  an  isolated  butte 
is  covered  by  the  brown  crust,  this  encrusted  portion 
is  protected,  while  the  lower  part  is  worn  away,  and 
a  mushroom-shaped  pillar  is  the  result.  The  stripping 
of  vertical  patches  of  the  crust  on  the  head  of  the 
mushroom  allows  of  the  formation  of  window-shaped 
cavities  on  the  sides  of  the  head,  and  projecting 
borders  are  frequently  produced.  Some  of  these 
mushroom -shaped  rocks  observed  by  Walther  were 
over  fifteen  feet  high,  the  brown  summit  occasionally 
projecting  about  a  yard  beyond  the  white  stalk. 

The    formation    of    valleys   in    desert    regions    is 


DESERTS  259 

effected  in  more  than  one  way.  The  buttes  of  the 
Bad  Lands  of  Wyoming  are  the  outstanding  portions 
of  rocks,  which  have  been  carved  into  small  valleys 
by  the  action  of  the  wind,  and  Walther  ascribes  the 
main  part  of  the  formation  of  the  wadys  of  the 
Egyptian  desert  to  this  cause,  and  believes  that 
water  plays  a  very  subordinate  part  in  their  pro- 
duction, though  the  effects  of  the  thunder  showers 
which  occur  there  must  not  be  overlooked.  In  some 
desert  regions,  as  that  of  Colorado,  rainfall,  though 
slight,  gives  rise  to  streams  and  rivers  which  produce 
the  characteristic  canons.  Owing  to  absence  of 
vegetation,  the  water  when  it  does  fall  is  given  off 
rapidly  and  not  slowly,  and,  accordingly,  can  effect 
much  transportation,  and  therefore  corrasion,  when 
the  declivity  is  sufficient,  whereas  owing  to  the 
infrequency  of  rain,  weathering  is  retarded.  It  is 
in  these  regions  that  we  find  the  steep-sided  gorges 
carved  out  of  the  arid  plateaux,  which  are  gradually 
cut  up  into  flat-topped  mesas  and  buttes,  of  which 
the  sides  are  terraced  by  alternation  of  softer  and 
harder  strata,  and  the  softer  strata  are  carved  into 
intricate  forms. 

"The  water  from  the  occasional  rainfalls  carves  out 
innumerable  little  sinuous  washes,  which,  in  descending, 
come  together,  forming  deep  gullies.  These  keep  on  joining 
others,  until  the  main  drainage  wurse  of  the  valleys  is 
reached.  Between  this  network  of  washes  are  correspond- 
ing ridges,  which  in  a  favourable  light  give  to  the  mesa-face 
the  appearance  of  an  elaborate  and  very  artistic  piece  of 
ornamental  carving." l 

1  The  above  quotation  is  from  W.  H.  HOLMES'  Geological  Report  of 
the  San  Juan  District ;  Ninth  Annual  Report  of  the  United  States 
Geological  and  Geographical  Sun-ey,  p.  256.  The  structure  is  figured 
in  Plate  XLI.  of  that  work. 


26o     SCIENTIFIC   STUDY   OF   SCENERY 

Accumulation  in  Deserts. — The  accumulations  and 
deposits  of  desert  regions  are  formed  in  hollows  of 
the  dry  land  and  on  the  floors  of  inland  lakes.  The 
most  extensive  accumulation  of  the  dry  land  is 
blown  sand,  which  often  covers  great  expanses  of 
a  desert.  The  surface  of  the  sand  is  often  irregular, 
owing  to  the  formation  of  sand-hills  or  dunes,  which, 
may  occur  with  intervals  of  the  underlying  rock 
showing  between  them,  or  may  merely  form  the 
summits  of  considerable  thicknesses  of  blown  sand. 
If  an  obstacle  exists  in  an  area  over  which  sand  is 
being  blown,  some  of  the  sand  will  be  arrested  by  the 
obstacle  and  form  a  little  heap  around  it,  especially 
if  the  wind  varies  in  direction.  Such  obstacles  are 
often  furnished  by  the  sparsely-scattered  plants 
which  can  grow  on  a  sandy  tract.  The  sand 
accumulates  around  these,  the  top  of  the  plant 
continues  to  grow  above  the  sand,  and  eventually 
a  little  mound  of  sand  is  produced,  from  the  centre 
of  which  the  plant  which  caused  the  formation  of 
the  hillock  projects.  If  the  plants  are  fairly  abun- 
dant a  very  characteristic  appearance  is  presented 
by  the  innumerable  monticules,  each  possessing  its 
tuft  of  vegetation.  Walther  figures  examples  of  these 
hillocks  (Neulinge),  which  have  been  formed  around 
tamarisks  in  the  desert  of  the  Sinaitic  Peninsula. 

Dunes  of  desert  sand  may  be  formed  without 
any  obstacle  other  than  that  furnished  by  the  sand 
itself,  as  shown  by  Vaughan  Cornish  in  a  paper 
which  treats  of  the  formation  of  different  kinds  of 
dunes  in  detail, — a  paper  from  which  many  of  the 
facts  recorded  below  are  extracted.1  Desert  sand 

1  CORNISH,  V.,  "On  the  Formation  of  Sand-dunes,"  Geographical 
Journal,  March,  1897. 


DESERTS 


261 


differs  to  some  extent  from  the  sand  of  coast  sand- 
hills or  sand-dunes,  in  that  the  sand  in  the  latter  has 
been  largely  sorted  by  sea  action,  while  desert  sand 
contains  particles  of  various  sizes,  from  large  grains 
to  particles  of  dust.  The  former  act  as  obstacles, 
and  when  the  wind  blows,  the  finer  dust  is  heaped  up 
against  the  coarse  grains  and  a  "ripple-mark"  is 
formed  on  the  surface  of  the  sand  ;  these  "  ripple- 
marks  "  do  not  differ  materially  from  dunes  save 
in  size.  The  structure  of  a  dune  is  largely  depend- 
ent upon  the  eddy  produced  on  the  lee-side,  as 
shown  in  Figure  37  (after  a  figure  by  Cornish), 


FIG.  37. 

which  represents  a  cross-section  of  two  dunes   and 
the  directions  of  the  air  currents. 

The  height  from  the  crest  of  the  dune  to  the 
bottom  of  the  trough  in  front  is  the  amplitude  of 
the  sand-wave  and  cannot  strictly  be  spoken  of  as 
the  height  of  the  dune,  as  part  of  the  hollow  is 
produced  by  excavation  and  not  by  piling  up  ;  it 
is  only  when  a  dune  rests  upon  rock  below  that  we 
can  confidently  speak  of  the  height  of  a  dune.  The 
windward  slope  in  the  central  part  is  one  which  will 
allow  grains  to  be  carried  up  by  the  wind  ;  the  lower 
part  of  the  lee-slope  is  produced  by  excavation  on 
the  part  of  the  eddy,  while  higher  up  is  a  straighter 
portion  due  to  slipping  of  the  incoherent  grains,  and 
this  slipping  may  also  modify  the  base  by  producing 


262    SCIENTIFIC   STUDY   OF   SCENERY 

a  talus-slope.  The  descending  air-current  at  the 
crest  of  the  windward  slope  rounds  off  the  upper 
part  of  that  slope,  and  the  lower  part  of  the 
windward  slope  is,  like  that  of  the  lee-slope,  ex- 
cavated by  the  eddy. 

"  Thus  the  normal  profile  left  by  the  rippling  of 
sand  by  wind  has  the  following  parts — viz.,  a  wind- 
ward slope,  consisting  of  a  concave  and  convex  curve, 
and  a  lee-slope,  consisting  of  a  straight  line  and  a 
concave  curve." 

Reversible  wind  tends  to  turn  the  top  of  the  dune, 
and  gives  rise  to  a  hill  which  is  steep  on  the  wind- 
ward slope  as  well  as  on  the  lee  side. 

The  dunes  grow  sideways  as  well  as  upwards, 
owing  to  the  opposition  of  the  direct  current  by 
an  eddy.  As  the  centre  of  the  dune  has  a  greater 
height  than  the  sides,  the  sides  travel  forwards  more 
rapidly  than  the  centre,  producing  a  crescent-shaped 
mound  with  the  horns  pointing  to  leeward.  This 
is  the  form  of  the  barchanes  or  medanos  of  many 
desert  regions.  They  may  be  produced  by  an 
obstacle,  or  where  part  of  a  current  of  air  is 
relatively  feebler  than  that  in  the  immediate  vicinity. 
When  the  wind  varies  in  direction  these  barchanes 
may  take  very  complex  shapes,  with  many  horn-like 
projections  pointing  in  different  directions. 

Dunes  may,  under  different  circumstances,  lie 
longitudinally  or  transversely  to  the  direction  of 
the  prevailing  wind,  the  longitudinal  type,  as  shown 
by  Dr.  Blanford,  being  associated  with  wind  of 
greater  force  than  that  which  determines  the  forma- 
tion of  the  transverse  type. 

When  stripes  of  wind  of  velocity  different  from 
that  of  the  wind  on  either  side  produce  barchanes, 


DESERTS  263 

and  the  amount  of  sand  in  the  sand-shower  sub- 
sequently increases,  the  whole  of  the  surface,  except 
the  deep  excavations  on  the  lee  side  of  the  bar- 
chanes,  may  be  blurred  or  smoothed  over,  when 
these  excavations  will  be  left  on  an  otherwise  level 
surface  of  land  as  horseshoe-shaped  hollows.  Such 
hollows,  known  as  fuljes,  occur  in  many  deserts. 

Dunes  vary  in  height,  but  cannot  grow  to  an  in- 
definite height,  for  the  work  of  the  wind  at  the 
summits  of  the  dunes  is  assisted  by  gravity,  while 
that  of  the  eddy  in  the  trough  is  opposed  by  gravity, 
and  accordingly,  after  a  time,  more  sand  is  accumu- 
lated in  the  troughs  than  can  be  piled  up  on  the 
crests.  When  this  occurs  the  general  height  of  the 
desert  is  increased,  and  great  thicknesses  of  sand 
may  be  accumulated  with  the  dunes  upon  their 
upper  surface.  The  highest  dunes  are  not  much 
over  600  feet  above  the  lowest  parts  of  the  troughs. 
The  character  of  one  of  these  sand  deserts,  in  which 
the  sand  has  been  accumulated  to  a  great  thickness, 
has  been  well  described  by  Captain  A.  H.  McMahon.1 

"  Marching  via  Darband  and  Amir  Chah,  we  kept  to 
the  north  of  the  Koh-i-Sultan,  Damodun,  and  other 
mountain  ranges.  At  times  our  journey  lay  through  wide, 
open,  level  plains  covered  with  black  gravel,  at  others  we 
floundered  our  weary  way  through  broad  expanses  of  deep 
sand-hills,  which,  near  Amir  Chah  and  other  places,  assumed 
the  proportions  of  formidable  sand-mountains.  All  the 
mountains  we  passed  were  apparently  volcanic.  .  .  . 
These  mountains  are  all  being  gradually  covered  up  and 
buried  in  sand,  which  is  relentlessly  creeping  further  and 
further  up  their  sides.  Many  are  already  completely 

1  McMAHON,  A.  H.,  "The  Southern  Borders  of  Afghanistan," 
Geographical  Journal^  April,  1897. 


264     SCIENTIFIC   STUDY   OF   SCENERY 

buried,  and  a  high  mountain  of  sand  marks  their  burial- 
place.  Others  have  their  black  peaks  just  appearing  out 
of  the  white  expanse  of  sand-slopes.  Here  and  there  a 
loftier  mass  still  towers  with  its  black  crags  high  above  the 
devouring  waste  around,  but  the  sand  banked  up  on  their 
sides,  in  places  sometimes  1000  or  2000  feet  above  the 
level  of  their  base,  foretells  a  similar  fate  in  store  for  them. 
The  general  effect  of  the  scene  they  present  is  weird  and 
unnatural  in  the  extreme." 

The  pebbly  deserts,  like  that  referred  to  by  Captain 
McMahon  as  covered  with  black  gravel,  are  in  many 
cases  the  residue  of  former  sand  deserts  from  which 
the  finer  particles  of  sand  have  been  subsequently 
blown  away. 

In  some  regions,  especially  those  which  lie  to 
windward  of  areas  which  have  formerly  received 
accumulations  of  fine  glacial  mud,  the  wind-borne 
material  consists  of  fine  dust,  which  may  be  accumu- 
lated upon  plains  or  in  the  depressions  between  hill- 
ranges,  giving  rise  to  steppes.  When  the  steppes  are 
plains  the  surface  is  flat,  but  when  the  fine  dust  is 
blown  into  depressions  between  hills  the  upper 
surface  of  the  dust  forms  a  catenary  curve.  The 
accumulations  which  have  been  formed  in  steppes 
are  known  as  loess,  and  there  is  evidence  that  in 
geologically  recent  times  steppe  conditions,  mark- 
ing widespread  dry  climate,  prevailed  over  much 
more  extensive  areas  than  those  which  are  now 
characterised  by  them.1  In  many  places  the  loess 
has  subsequently  been  carved  by  water  action  into 
deep  canon-like. gorges,  as  in  some  parts  of  China. 

1  For  a  discussion  on  the  origin  of  the  loess,  see  a  paper  by  Baron 
VON  RICHTHOFEN,  Geological  Magazine,  decade  ii.,  vol.  ix.  (1882), 
P-  29:- 


DESERTS  265 

Loam  deserts  frequently  mark  the  sites  of  ancient 
lakes,  some  of  which  possessed  no  outlet,  as  already 
stated  when  noticing  the  character  of  some  of 
the  Bad  Lands  of  the  western  territories  of  North 
America.  These  desert  lakes  often  present  features 
of  interest.  If  the  rainfall  be  insufficient  to  fill  a 
depression  to  the  height  of  the  lowest  point  of  out- 
let from  the  depression,  the  lake  will  have  no  outlet 
and  its  level  will  fluctuate,  owing  to  variations  in  the 
rainfall  of  the  region,  for  much  of  the  water  is  re- 
moved by  evaporation.  Accordingly  we  find  well- 
marked  shore  lines  accumulated  where  the  surface 
was  fairly  constant  in  height  for  a  sufficient  time 
to  allow  of  the  accumulation  of  a  beach.  These 
lines  of  beach  form  a  striking  feature  on  the  hill-sides 
around  the  Great  Salt  Lake  of  Utah  and  neigh- 
bouring lakes  of  the  same  region,  and  they  have 
been  frequently  described  and  figured.  » 

When  complete  desiccation  of  these  lakes  occurs 
the  salts  which  were  in  solution  in  the  water  are 
deposited  in  crystalline  sheets,  often  appearing  like 
surfaces  of  ice  in  the  desert.  Such  tracts  of  salt 
are  found  in  the  Shats  of  Algeria,  and  McMahon 
describes  similar  expanses  in  the  southern  border- 
lands of  Afghanistan. 

Accumulations  of  salt  may,  however,  be  formed  in 
desert  regions  without  the  formation  of  a  lake.  The 
thundershowers  of  many  deserts  carry  salt  from  the 
rocks  to  a  lower  level,  and  as  the  water  evaporates 
the  salt  is  left  behind,  and  in  this  way  sheets  of  salt 
may  accumulate  in  depressions.  Again,  it  has  been 
seen  that  salt  may  be  brought  to  the  surface  by 
capillary  action,  and  accordingly  we  find  some  deserts, 
like  the  alkali  deserts  of  North  America,  characterised 


266    SCIENTIFIC   STUDY   OF   SCENERY 

by  coatings  of  salt,  which  form  a  whitish  crust  upon 
the  surface  of  the  ground.1 

A  word  may  be  said  concerning  the  atmospheric 
conditions  of  a  desert  region.  Owing  to  the  extra- 
ordinary dryness  of  the  atmosphere  the  traveller  can 
frequently  see  objects  at  great  distances.  Of  the 
desert  on  the  borders  of  Afghanistan,  Captain 
McMahon  writes,  "The  clear,  dry,  sparkling  atmo- 
sphere, the  deep  blue,  cloudless  skies  of  the  greater 
part  of  the  year,  and  the  almost  boundless  horizons 
produce  feelings  of  exhilaration  and  a  sense  of  free- 
dom which  go  far  to  make  up  for  the  shortcomings 
of  the  country  in  other  respects." 

The  mirage  of  the  desert,  like  that  of  other  regions, 
as  the  polar  areas,  the  English  fenlands,  and  the 
Lake  of  Geneva,  is  due  to  reflection  from  the  surface 
of  a  stratum  of  air,  where  originally  horizontal 
strata  of  different  densities  have  been  disturbed  by 
differential  heating  or  cooling  from  underneath. 
The  reader  who  wishes  for  a  fuller  account  of  the 
phenomena  of  mirage  may  consult  a  paper  by 
Professor  Everett  in  Nature,  November  I9th  and 
27th,  1874. 

Sand-storms  occur  during  the  prevalence  of  strong 
winds  in  desert  regions.  They  may  be  due  to 
wind  blowing  in  one  direction  over  wide  areas  when 
the  sand  is  wafted  on  by  the  wind,  and  in^  these 
conditions  sand-dunes  are  formed  and  increased  in 
size.  Some  of  the  most  remarkable  and  destructive 
sand-storms  are  cyclonic  whirls  of  comparatively 
small  size,  which  produce  sand-pillars  and  cupola- 
shaped  masses  of  sand,  often  miles  in  diameter ;  the 

1  See  GEIKIE,  Sir  A.,  Geological  Sketches  at  Home  and  Abroad, 
p.  240,  fig.  25. 


DESERTS  267 

general  circular  mass  may  be  complicated  by  minor 
spiral  columns  due  to  subsidiary  spiral  rotation 
of  the  wind  on  the  margin  of  the  main  cyclone. 

It  has  already  been  stated  that  desert  conditions 
are  largely  due  to  the  general  absence  of  vegeta- 
tion, but  that  which  does  exist  in  a  desert  has 
a  character  of  its  own,  and  produces  considerable 
effect  upon  the  scenery  of  those  portions  of  desert 
which  are  occupied  by  a  scant  growth  of  vegetation. 
There  are  decided  resemblances  between  the  flora 
of  the  desert  and  that  of  high  alpine  or  of  arctic 
regions,  and  the  resemblances  are  due  to  the  existence 
of  similar  physical  conditions  in  desert  and  arctic 
areas,  namely,  long  periods  of  dryness  alternating 
with  short  periods  when  there  is  a  considerable 
supply  of  moisture.  In  arctic  regions  the  dryness 
is  due  to  cold  and  wind,  and  the  moisture  is  supplied 
by  melting  of  snow.  In  the  desert  the  dryness  is  due 
to  heat  and  drought ;  the  moisture  is  supplied  during 
the  short  periods  of  rainfall  and  to  some  extent  by 
night  dews. 

One  effect  of  desert  climate  is  that  the  plants 
occur  in  comparative  isolation,  often  with  considerable 
intervals  of  barren  ground  intervening  between  indi- 
vidual plants.  Furthermore  there  is  usually  a  special 
modification  of  the  leaves  of  the  plants,  which  enables 
them  to  resist  the  long  periods  of  drought.  The  leaves 
are  often  scaly,  sword- shaped  or  tufted,  occurring  in 
rosette-like  growths ;  sometimes  they  are  modified 
into  thorns,  and  in  some  cases  shoots  devoid  of  leaves 
are  found.  The  prevailing  colour  of  the  desert  plants 
is  grey-green,  dirty  green,  or  grey-white.  Succulent 
plants,  however,  are  frequently  found,  and  some  deserts 
possess  a  considerable  variety  of  flowering  plants. 


268     SCIENTIFIC   STUDY   OF   SCENERY 

In  the  Egypt-Arabian  desert  the  leaves  of  the 
grasses  are  short  and  stiff;  plants  with  shoots  devoid 
of  leaves  occur,  as  Ephedra  ;  in  Tamarix  the  leaves 
are  modified  into  scales,  and  there  are  several  thorny 
plants.  Many  bulbous  plants  are  found,  and  in 
some  parts  flowering  plants  produce  an  effect  upon 
the  scenery,  thus  the  storksbill  {Erodium}  when  in 
flower  gives  a  red  hue  to  tracts  where  it  grows. 

The  remarkable  edible  lichen  Parmelia  esculenta, 
supposed  to  be  the  manna  of  the  Scriptures,  grows 
in  the  desert  from  Central  Asia  to  Algeria;  fragments 
of  it  are  detached  from  the  rocks  by  the  wind,  and 
these  fragments  are  blown  into  other  places. 

In  the  Kalahari  desert  of  South  Africa  many  of  the 
plants  possess  tubers  mimicking  stones.  There  are 
many  bulbous  plants  and  various  succulent  plants, 
as  spurges  (Euphorbiaceae) ;  also  xerophilous  plants, 
that  is,  plants  which  flourish  in  a  dry  climate,  as 
Mimosa  and  various  Proteaceae. 

In  Australia  parts  of  the  desert  are  occupied  by 
the  isolated  stool-like  masses  of  Triodia,  there  called 
Spinifex,  with  a  few  needle-like  spikes  projecting,  as 
seen  in  the  plate  copied  by  permission  of  the  author 
and  of  the  Council  of  the  Geographical  Society,  from 
a  figure  illustrating  a  paper  by  the  Hon.  D.  W. 
Carnegie,  "Explorations  of  the  Interior  of  Western 
Australia."1 

In  North  America  the  deserts  are  rendered  mono- 
tonous by  the  prevalent  sage-brush,  consisting  of 
various  species  of  Artemisia,  especially  A.  tridentata. 
An  interesting  feature  of  these  deserts  is  the  sudden 
change  from  highlands,  supplied  with  abundant  water 
and  rich  in  vegetation,  to  desert  lowlands.  Mr.  H. 

1  Geographical  Journal,  March,  1898  (vol.  xi.). 


DESERTS  269 

Gannett  thus  speaks  of  the  Uncompahgre  plateau,  in 
the  Grand  River  District1: — 

"  Nowhere  is  the  influence  of  vegetation  on  the  character 
of  the  vegetation  more  plainly  marked  than  on  this  plateau. 
In  the  interior,  near  the  crest,  the  land  is,  to  the  Utes,  one 
flowing  with  milk  and  honey.  Here  are  fine  streams  of 
clear,  cold  water,  beautiful  aspen  groves,  the  best  of  grass 
in  the  greatest  abundance,  and  a  profusion  of  wild  fruits 
and  berries,  while  the  country  is  a  perfect  flower-garden. 
This  extends  as  low  as  7000  feet,  below  which  the  scene 
changes  to  one  in  all  respects  the  reverse.  Aspen  gives 
place  to  pinon  and  cedar ;  the  grasses,  fruits,  and  flowers,  to 
sage,  cacti,  and  bare  rock.  The  streams  become  confined 
in  rocky  canons,  turn  muddy  and  warm,  and  gradually 
disappear.  The  game  changes,  black-tailed  deer  give  place 
to  the  white-tailed  species.  Grouse  disappear,  while  rattle- 
snakes and  centipedes  assert  their  proprietorship.  In  the 
place  of  an  open,  rolling  country,  we  enter  a  district  traversed 
by  deep,  narrow  gorges,  of  abrupt  precipices,  a  country 
difficult  in  the  extreme  to  traverse  without  a  knowledge  of 
its  few  highways." 

I  have  already  quoted  part  of  Sir  A.  Geikie's 
description  of  the  scenery  of  the  North  American 
Bad  Lands.  Here  is  an  additional  extract  from  that 
writer's  account : — 

"There  is  a  further  feature  which  crowns  the  repulsive- 
ness  of  the  Bad  Lands.  There  are  no  springs  or  streams. 
Into  the  soil,  parched  by  the  fierce  heats  of  a  torrid  summer, 
the  moisture  of  the  subsoil  ascends  by  capillary  attraction, 
carrying  with  it  the  saline  solutions  it  has  extracted  from 
the  rocks.  At  the  surface  it  is  at  once  evaporated,  leaving 
behind  a  white  crust  or  efflorescence,  which  covers  the  bare 
ground  and  encrusts  the  pebbles  strewn  thereon.  Vegeta- 

1  Report  U.S.  Geological  and  Geographical  Survey,  1875,  P-  34°« 


270    SCIENTIFIC   STUDY   OF   SCENERY 

tion  wholly  fails,  save  here  and  there  a  bunch  of  salt-weed  or 
a  bush  of  the  ubiquitous  sage-brush,  the  parched  livid  green 
of  which  serves  only  to  increase  the  desolation  of  the 
desert." 

In  these  alkali  deserts,  and  indeed  in  any  desert 
where  there  is  a  considerable  amount  of  salt,  the 
flora  frequently  presents  resemblances  to  that  of  the 
salt-marshes  around  the  sea-coast.  Besides  cacti  and 
spurges,  which  also  grow  in  the  sand  deserts,  we  find 
marsh-samphire  (Salicornia],  plantains  (Plantago),  and 
various  representatives  of  the  Chenopodiaceae  or  goose- 
foot  plants. 

Oases  occur  wherever  water  issues  from  the  ground 
to  a  sufficient  degree  to  support  vegetation.  The 
water  may  be  due  to  various  causes,  as  relatively 
large  amount  of  rainfall  in  some  localities,  or  course 
of  the  underground  water.  The  latter  is  probably 
often  a  cause  of  oases,  as  indicated  by  their  frequent 
occurrence  along  definite  lines,  a  distribution  which 
often  determines  the  routes  of  caravans.  Various 
plants  grow  in  these  oases,  including  trees.  In  North 
Africa  the  date-palm  is  the  only  indigenous  tree, 
though  others  have  been  introduced  by  man.1 

Though  the  production  of  desert  features  on  a 
large  scale  requires  a  dry  climate,  we  find  that  an 
imitation  of  many  of  the  characteristic  features  of  a 
desert  region  may  be  developed  in  our  own  country 
upon  a  small  scale.  The  nature  of  the  sand-dunes 
of  the  coasts  is  similar  in  general  characters  to  that 
of  the  desert  dunes,  and  some  of  the  attributes  of 

1  For  a  fuller  account  of  the  vegetation  of  deserts  the  reader  may 
consult  E.  WARMING'S  Lehrbtich  der  okotogischen  Pflanzengeographie, 
Berlin,  1896. 


DESERTS  271 

desert  vegetation  occur  among  the  plants  of  our 
coastal  dunes.  Tracts  even  more  suggestive  of  sand 
deserts  are  found  in  some  parts  of  East  Anglia,  at 
some  distance  from  the  sea,  where  the  superficial 
deposits  are  formed  of  incoherent  sand,  which  is 
readily  blown  about  by  the  wind. 

The  alkaline  and  salt  flats  of  desert  regions  have 
some  resemblances  to  the  salt  marshes  which  occur 
in  many  of  our  estuaries ;  they  are  particularly  well 
developed  in  the  estuaries  around  Morecambe  Bay, 
though  some  of  these  have  been  modified  by  culti- 
vation. It  has  already  been  stated  that  several  of 
the  plants  of  salt-deserts,  as  Salicornia  and  Cheno- 
podiaceae,  are  also  found  in  these  maritime  salt 
marshes. 

Lastly  we  find  simulation  of  rock  deserts  on  a 
small  scale  among  the  Yorkshire  moors,  where  the 
millstone  grit,  being  very  absorbent,  frequently 
engulfs  the  rain-water  as  it  descends,  thereby 
limiting  surface  erosion  by  water,  and  causing 
chemical  weathering,  effect  of  change  of  temperature 
and  wind  to  become  dominant  agents  of  sculpture. 
It  is  in  such  regions  (as  already  noted  in  Chapter 
VIII.)  that  we  find  miniature  representations  of  the 
wind-worn  rocks  of  deserts,  as,  for  instance,  the 
Brimham  Rocks,  near  Knaresborough,  and  the  Cow 
and  Calf  at  Ilkley. 


CHAPTER   XVI. 
FROST,   SNOW,   AND   ICE 

ALTHOUGH  it  is  in  alpine  and  arctic  regions 
that  the  scenic  effects  due  to   frost  are   most 
striking,  the  effects  of  frost  in  a  country  like  Britain, 
under  its  present  climatic  conditions,  are  far  from 
insignificant. 

The  first  point  to  notice  in  connexion  with  frost  is 
the  exceptional  behaviour  of  water  as  it  is  cooled 
down  towards  the  freezing-point.  It  is  well  known 
that  water  contracts  when  cooled  until  it  possesses 
a  temperature  of  39°  Fahrenheit,  when  it  expands, 
and  accordingly  grows  lighter.  At  a  temperature 
of  32°  Fahrenheit,  the  freezing-point  of  fresh  water, 
the  change  from  the  liquid  to  the  solid  condition 
is  accompanied  by  a  very  considerable  expansion 
(about  one-fourteenth  of  its  volume).  One  notice- 
able result  of  this  expansion  is  the  efficacy  of  frost 
as  an  agent  of  disintegration  of  rocks,  as  described 
in  a  preceding  chapter.  Another  effect  of  great 
significance  from  the  scenic  point  of  view  is  that, 
owing  to  expansion  occurring  above  freezing-point, 
the  top  water,  after  its  temperature  is  reduced  to 
39°  Fahrenheit,  becomes  lighter,  and  therefore  re- 
mains on  the  surface,  so  that  the  surface  water 
freezes  first,  whereas,  if  contraction  occurred  as  the 
temperature  was  lowered  to  the  freezing-point,  the 
272 


FROST,   SNOW,   AND    ICE  273 

cold  water  would  continue  to  sink  to  the  bottom, 
and  the  whole  of  a  water  area  would  be  gradually 
lowered  to  freezing-point,  and  a  lake  might  thus  be 
frozen  solid,  whereas,  under  the  actual  conditions 
which  exist,  the  ice  is  formed  upon  the  surface,  and 
seldom  extends  to  a  very  great  depth  in  deep  sheets 
of  water.1 

Water,  like  many  other  liquids,  when  consolidated, 
assumes  a  crystalline  condition,  the  crystals  belonging 
to  systems  termed  by  mineralogists  the  hexagonal 
and  rhombohedral  systems,  and  the  compound 
crystals  are  also  arranged  in  symmetrical  shapes  as 
well  exhibited  in  many  snowflakes,  which  show 
various  six-rayed  forms.  The  crystalline  structure 
may  also  be  frequently  seen  in  the  products  of  hoar- 
frost and  in  other  cases  where  consolidation  has  taken 
place  under  conditions  favourable  for  the  free  growth 
of  the  crystal-outlines,  but  even  when  invisible  it  is 
there,  for  instance,  in  the  ice  on  the  surface  of  a  pond, 
as  may  be  proved  by  suitable  experiments.  The 
beautiful  patterns  seen  on  our  windows  on  a  frosty 
morning  owe  their  beauty  to  the  consolidation  of 
water  in  a  crystalline  condition.  We  may  here 
briefly  notice  some  of  the  processes  resulting  in 
the  formation  of  ice  which  give  rise  to  minor  or 
transient  effects  upon  scenery. 

Hoar-frost  is  produced  when  the  dew-point  is 
below  freezing-point,  when  the  aqueous  vapour  is  not 
condensed  into  minute  drops  of  water,  but  the  solid 
form  is  assumed.  Hoar-frost,  like  dew,  forms  best 
on  substances  which  are  good  radiators  of  heat,  and 
accordingly  it  is  prone  to  be  formed  on  vegetation, 

1  The  exceptional  conditions  controlling  the  formation  of  "ground- 
ice,"  or  "  anchor  ice,"  on  the  floors  of  water  areas  do  not  concern  us. 
T 


274    SCIENTIFIC   STUDY   OF   SCENERY 

hence  giving  rise  to  the  picturesque  appearance 
presented  by  trees  which  are  laden  with  it. 

Warm  vapour-laden  air  coming  in  contact  with 
frozen  ground  may  have  its  vapour  condensed  and 
deposited  in  the  solid  form  as  "  glazed  frost "  or 
"verglas,"  which  is  specially  remarkable  when  rain 
falls.  An  interesting  case  of  verglas  is  quoted  from 
the  Comptes  Rendus  of  the  French  Academy  by 
Dr.  R.  H.  Scott,  in  his  work  on  Elementary  Meteor- 
ology, chapter  vii.  In  mountain  regions  very  re- 
markable effects  are  often  produced,  owing  to  the 
formation  of  ice  crystals  which  are  deposited  on 
cold  surfaces  when  a  warm  vapour-laden  wind 
strikes  against  them.  Irregular  blocks  of  stone 
become  covered  with  thick  masses  bristling  with 
crystalline  projections,  and  often  assume  very  bizarre 
forms.  This  phenomenon  may  often  be  seen  on  our 
own  hills  in  the  winter  and  early  spring  months,  but 
in  higher  latitudes  or  on  higher  altitudes  it  may  be 
observed  in  the  summer  months.  Mr.  Garwood 
noticed  a  very  striking  case  on  Hornsund  Tind, 
Spitsbergen.  The  projections,  some  of  which  were 
eighteen  inches  in  length,  grew  out  from  a  vertical 
face  of  cliff  during  about  three  weeks  of  continuous 
fog. 

Ice  is  not  only  produced  by  contact  of  warm 
moisture-laden  air  with  cold  ground,  but  by  the 
contact  of  cold  air  with  warm  ground.  Owing  to 
the  fact  that  the  air  is  not  directly  heated  by  the 
rays  from  the  sun,  but  by  the  dark  heat  which  is 
given  off  from  the  earth,  we  often  find  the  earth's 
surface  is  warm  when  the  temperature  of  the  air 
around  is  below  freezing-point.  Accordingly  any 
snow  or  ice  which  is  resting  on  the  earth  may  be 


FROST,   SNOW,   AND    ICE  275 

melted,  and  if  it  is  resting  on  a  projecting  surface 
the  water  will  flow  down  and  hang  as  a  drop  on  the 
edge  of  the  projection.  The  contact  of  the  cold  air 
may  cause  this  drop  to  freeze  when  it  is  at  rest,  and 
the  next  water  which  descends  will  swathe  this  drop 
with  moisture,  which,  freezing  in  turn,  will  increase 
the  diameter  of  the  frozen  knob,  while  more  water, 
hanging  from  the  extremity  of  the  previously  frozen 
drop,  will  in  turn  freeze,  thus  lengthening  the  frozen 
mass.  By  a  continuation  of  the  process  an  icicle  is 
formed,  much  as  a  stalactite  of  carbonate  of  lime  is 
formed  under  the  arch  of  a  bridge  or  on  the  roof  of 
a  cavern.  Large  masses  of  pendent  icicles  are  often 
thus  formed  in  the  neighbourhood  of  waterfalls  or  at 
the  edges  of  overhanging  banks  of  a  stream.  In 
mountain  regions,  conditions  favourable  for  their 
formation  occur  in  the  interior  of  the  fissures  or 
crevasses  of  glaciers,  and  also  on  the  under  surfaces 
of  snow  cornices,  the  mode  of  formation  of  which 
will  be  subsequently  considered. 

The  effects  of  hailstorm,  though  often  very  de- 
structive, are  not  of  great  interest  to  the  student 
of  scenery,  and  we  may  now  pass  on  to  consider  the 
formation  and  mode  of  accumulation  of  snow. 

Snow,  as  is  well  known,  is  not  frozen  rain ;  the  snow- 
flakes  are  formed  from  aqueous  vapour  by  consolida- 
tion before  the  vapour  has  given  place  to  definite  liquid 
drops.  Snow  will  collect  at  the  door  of  a  crowded 
railway  carriage  containing  foot-warmers,  owing  to  the 
consolidation  of  the  aqueous  vapour  in  the  carriage 
by  the  cold  air  coming  through  the  apertures  at  the 
sides  of  the  door,  without  any  perceptible  liquid 
water  being  formed  previously,  and  the  story  of  the 
St.  Petersburg  ball,  where  snow  began  to  fall  in  the 


276     SCIENTIFIC   STUDY   OF   SCENERY 

overheated  room  when  the  windows  were  broken  to 
let  in  air,  is  often  quoted. 

The  amount  of  snow  which  falls  during  a  severe 
storm  is  often  exaggerated,  as  the  thickness  of  drifted 
snow  is  frequently  taken  as  representing  the  thick- 
ness of  the  actual  fall.  According  to  Dr.  Scott 
a  foot  of  snow  yields  about  an  inch  of  rain,  and  as 
a  fall  of  three  inches  of  rain  in  a  day  is  a  rare  event 
in  most  parts  of  our  island,  statements  of  the  fall  of 
many  feet  of  snow  during  one  snowstorm  must  be 
received  with  caution. 

Snow  is  readily  drifted  by  the  wind,  and  collects 
in  places  where  the  force  of  the  wind  is  diminished, 
so  that  a  snowdrift  may  in  many  ways  be  compared 
to  a  sand-dune ;  not  altogether,  however,  for  Mr. 
Cornish  states  in  the  discussion  upon  his  paper  on 
"  The  Formation  of  Sand-dunes  "  that  some  observa- 
tions which  he  has  made  "  show  curious  differences 
between  the  tactics  of  drifting  snow  and  those  of 
blown  sand."  The  effect  of  regelation,  that  property 
of  ice  which  causes  two  pieces  to  cohere  when  in 
contact,  must  no  doubt  be  taken  into  account  when 
discussing  the  causes  for  the  actual  outlines  of 
snowdrifts,  as  proved  by  the  existence  of  snow 
cornices,  which  are  portions  of  drifted  snow  pro- 
jecting over  the  leeward  side  of  mountain-ridges  and 
summits,  owing  to  the  consolidation  of  the  snow 
particles.  These  snow  cornices  to  some  extent 
record  the  existence  of  the  wind  eddies  which  are 
formed  on  the  leeward  sides  of  obstacles ;  they  have 
a  convex  curve  at  the  top,  arching  over,  and  a 
concave  curve  below  where  the  eddy  must  exercise 
a  destructive  effect.  They  may  project  many  feet 
beyond  the  actual  rocky  ridge  of  the  mountain, 


FROST,   SNOW,   AND    ICE  277 

and  when  fringed  with  icicles  form  very  remarkable 
objects. 

In  some  parts  of  the  world  snow  is  unknown,  in 
other  parts  it  only  falls  at  intervals  in  winter  and 
rapidly  melts,  while  in  other  parts  the  snow  lies 
all  the  year  round.  The  elevation  at  which  the 
annual  amount  of  snowfall  is  just  the  same  as  the 
annual  amount  of  snow  melted  is  known  as  the  snow- 
line,  and  above  it  are  the  regions  of  perpetual  snow. 
As  is  well  known,  the  altitude  of  the  snow-line  varies 
according  to  latitude,  though  local  variations  often 
produce  modifications ;  nevertheless  in  any  one 
district  the  general  level  often  approaches  the 
horizontal  so  nearly  that  when  viewed  from  a 
distance  a  horizontal  straight  line  appears  to  be 
ruled  across  the  mountains  above  which  is  perpetual 
snow,  and  below  which  there  is  practically  none. 

At  the  equator  the  snow-line  has  a  height  of  about 
16,000  feet,  in  the  Alps  it  lies  at  about  9000  feet, 
in  Norway  at  5000  feet,  while  at  Spitsbergen  it  has 
fallen  to  a  few  hundred  feet  above  sea-level.  It 
must  not  be  supposed,  however,  that  all  elevations 
above  the  snow-line  are  covered  with  snow.  When 
the  slope  of  the  ground  is  very  great  the  snow  can 
only  lie  in  patches  on  the  ledges  and  gentler  slopes, 
or  collect  in  the  couloirs  and  gullies.  Thus  it  is  that 
many  of  the  Alpine  peaks,  as  the  Matterhorn,  rise 
above  the  snow  fields  as  rocky  eminences,  only 
scarred  here  and  there  with  snow.  Owing  to  this, 
and  as  the  gullies  and  variations  of  slope  are  usually 
dependent  upon  geological  structure,  we  can  often 
learn  much  of  the  anatomy  of  a  mountain  by  ob- 
servation of  the  lie  of  the  snow,  and  this  is  the 
case  also  in  regions  below  the  snow-line  if  we 


278     SCIENTIFIC   STUDY   OF   SCENERY 

examine  them  when  snow  has  fallen.  Thus  the 
direction  of  the  main  lines  of  stratification  and 
jointing  is  often  indicated  by  lines  of  snow  on  a 
mountain.  Again,  as  certain  rocks  during  the 
melting  of  the  snow  absorb  the  water  more  quickly 
than  others,  the  snow  will  lie  on  these  absorbent 
rocks  for  a  longer  time  than  on  other  rocks,  where 
the  water  being  left  on  the  surface  dissolves  the 
snow.  Thus  in  early  spring  the  western  slopes  of 
the  Pennine  Chain  facing  the  Eden  Valley  are  often 
marked  by  long  horizontal  bands  of  dark  rock 
practically  devoid  of  snow,  separated  from  one 
another  by  snowy  strips.  These  dark  lines  mark 
the  shales,  which,  owing  to  their  impervious  nature, 
keep  the  water  on  the  surface,  while  the  intervening 
white  strips  are  beds  of  grit,  which  retain  the  snow, 
though  the  grit  slopes  are  often  actually  steeper  than 
those  occupied  by  shale.1 

The  effect  of  slope  on  the  accumulation  of  snow 
may  be  well  illustrated  by  contrasting  the  snowy 
dome  of  Mont  Blanc  with  the  rocky  pinnacles  of 
its  attendant  Aiguilles,  the  latter  being  at  an  eleva- 
tion inferior  to  that  of  the  topmost  dome. 

Ice  is  often  formed  on  mountain  sides,  adhering 
to  the  rocks  in  extensive  sheets,  which  lie  at  an 
angle  far  greater  than  that  at  which  loose  snow 
will  repose.  These  ice  slopes  are  well  known  to 
Alpine  climbers,  and  they  often  present  a  marked 
feature  in  the  scenery. 

The  snow -line  being  the  elevation  at  which  the 
annual  amount  of  snowfall  is  just  the  same  as  the 
amount  of  snow  melted,  it  follows  that  above  the 

1  For  effect  of  joints  in  retaining  snow,  see  Meddehlser  om  Gronland, 
Part  II.,  Plate  VII.  (facing  p.  164). 


FROST,   SNOW,   AND    ICE  279 

snow -line  more  snow  falls  annually  than  is  melted, 
and  accordingly  the  snow  of  one  year  would  tend 
to  remain  and  be  added  to  the  snow  of  the  preceding 
year.  Does  this  accumulation  go  on  indefinitely? 
If  it  did,  the  higher  regions  would  in  time  become 
buried  in  vast  accumulations  of  snow.  But  there 
are  other  ways  besides  actual  melting  by  which  the 
heights  are  rid  of  an  excess  of  snow.  We  have 
seen  that  snow  is  not  frozen  rain,  that  the  particles 
are  frozen  before  they  form  liquid  drops,  and  similarly 
snow  may  disappear  without  the  production  of 
appreciable  masses  of  water  on  the  surface.  During 
a  prolonged  frost  snow  that  has  fallen  before  the 
frost  commenced,  or  at  an  early  period  of  the  setting 
in  of  frosty  conditions,  may  be  observed  to  diminish, 
and  it  may  even  disappear,  without  any  appreciable 
liquefaction,  just  as  a  mass  of  camphor  does.  The 
process  is  known  as  sublimation,  and  owing  to  it 
some  snow  is  vaporised  even  above  the  snow  line. 
Again,  on  comparatively  steep  slopes,  as  the  snow 
accumulates,  large  masses  may  break  off  and  fall 
to  a  lower  level  as  snow  avalanches.  These 
avalanches  are  well  known  in  mountain  regions ; 
their  fall  is  very  impressive,  and  the  piled-up  banks 
of  avalanche  snow  frequently  form  a  marked  feature 
at  the  bases  of  the  slopes  from  which  they  have 
fallen.  But  just  as  the  superabundant  rain  of  upland 
regions  is  carried  to  the  lowlands  by  rivers,  the 
superabundant  snow  of  highlands  is  chiefly  brought 
to  a  lower  level  by  those  icy  rivers  named  glaciers, 
the  nature  of  which  we  must  now  consider.  % 

In  order  that  glaciers  may  exist,  there  must  be 
conditions  in  an  area  favourable  for  their  formation, 
and  cold  is  the  condition  which  naturally  strikes  one 


280    SCIENTIFIC   STUDY   OF   SCENERY 

as  most  important ;  no  glacier  can  be  formed  unless 
the  temperature  is  sufficiently  low  to  allow  of  the 
accumulation  of  a  considerable  quantity  of  snow. 
Secondly,  the  amount  of  aqueous  vapour  which  is 
brought  to  the  region  from  elsewhere  must  be  large, 
in  order  to  supply  material  for  the  production  of 
snow.  However  cold  a  region  may  be,  if  it  is  also 
dry  there  will  be  no  appreciable  snowfall,  and 
accordingly  no  glaciers.  The  importance  of  the 
supply  of  aqueous  vapour  is  well  illustrated  by  the 
Alaskan  glaciers.  The  great  glaciers  of  Alaska 
occur  in  the  south,  where  the  warm,  moisture-laden 
winds  of  the  Pacific  Ocean  strike  the  land,  and  are 
responsible  for  a  large  snowfall,  and  not  further  to 
the  north,  though  it  is  colder,  for  there  the  winds 
have  been  robbed  of  much  of  their  aqueous  vapour, 
and  blow  over  the  colder  tracts  as  dry  winds. 
Thirdly,  the  physical  conditions  must  be  favourable 
for  the  accumulation  of  snow.  It  is  clear  that 
glaciers  or  the  snow  necessary  for  their  production 
cannot  form  on  a  vertical  cliff,  and  it  is  doubtful  how 
far  the  movement  which  characterises  glaciers  could 
occur  as  the  result  of  an  accumulation  of  snow 
formed  on  level  ground.  It  is  among  the  inequalities 
of  a  mountainous  region  that  we  find  the  conditions 
most  favourable  for  the  accumulation  of  snow  which 
will  give  rise  to  glaciers. 

That  glaciers  move  is  well  known  to  everyone,  one 
very  significant  indication  of  their  movement  being 
furnished  by  the  fact  that  they  often  descend  far 
belpw  the  snow-line.  Herein  lies  one  of  the  most 
striking  features  of  these  ice-rivers  from  the  point  of 
view  of  the  student  of  scenery,  for  we  frequently  find 
a  marked  contrast  between  the  great  tongue  of  ice 


FROST,   SNOW,   AND    ICE  281 

at  the  extremity  of  a  glacier  and  its  immediate 
surroundings.  The  terminal  face  of  the  ice  of  the 
Tasman  glacier  in  New  Zealand  is  about  700  feet 
above  sea  level,  and  it  "  is  hidden  by  a  grove  of 
Pines,  Ratas,  Beeches,  and  arborescent  Ferns  in  the 
foreground."1 

As  we  ascend  a  glacier  from  its  termination 
toward  the  watershed,  we  find  the  lower  part  below 
the  snow-line  devoid  of  snow  and  consisting  of  ice. 
Higher  up  the  ice  is  covered  by  unmelted  snow,  the 
junction  of  the  snowy  and  snowless  portions  being 
sometimes  irregular,  though  there  is  often  a  marked 
contrast  between  the  two  portions  as  seen  from  a 
distance.  Proceeding  still  higher  the  glacier  ice  is 
found  to  be  replaced  by  a  granular  substance  in- 
termediate between  snow  and  ice,  known  as  neve  or 
firn,2  and  yet  higher  the  neve  gives  place  to  ordinary 

1  HOCHSTETTER'S  New  Zealand,  quoted  by  A.  C.  SEWARD,  Fossil 
Plants  as  Tests  of  Climate.     Cambridge,  1892. 

2  The  following  description  of  the  appearance  of  a  Swiss  neve  is 
from  the  pen  of  Principal  Forbes  (Edinburgh  Revieiv,  April,  1842). 
"  The  neve  or  firn  is  the  unconsolidated  glacier.     As  we  approach 
it  the  fissures  of  the  glacier  become  generally  rarer  and  always  narrower. 
The  elevation  above  the  sea  being  already  very  considerable,  perhaps 
8000  or  9000  English  feet,  the  winter's  snow  lies  all  summer  on  the 
surface  of  the  ice,  conceals  the  crevasses,  and  partly  also  the  structure 
of  the  matter  of  the  glacier  itself ;    to  discern  which  the  snow  must 
be  carefully  removed.    It  is  a  frequent,  perhaps  a  general,  characteristic 
of  the   transition   from   the   glacier  proper  to  the  neve,   that  whilst 
the  former  presents  a  convex  surface  the  latter  is  concave,  and  inos- 
culates insensibly  into  the  snowy  steeps  which  clothe  the  sides  of  the 
upper  glacier  basins  at  these  great  heights.    Magnificent  is  the  prospect 
which   these   firns   sometimes   present.     The   surface   is   smooth   and 
almost  level,  like  an  artificial  floor  stretched  across  a  valley,  whose 
sides  evidently  descend  to  a  great  depth  beneath.     It  is  a  real  platform 
— to  compare  great  things  with  small,   it  is  a  theatre  with  the  pit 
boarded  over ;  and  what  a  theatre  !      From  that  even,  snowy  carpet 
of  dazzling  white  rise  hundreds  of  nameless  peaks  on  either  hand, 
seeming  to  pierce  a  sky  whose  azure  hue  is  so  intense  as  to  find  no 


282     SCIENTIFIC   STUDY   OF   SCENERY 

snow.  How  does  the  change  from  snow  to  neve"  and 
from  this  to  glacier  ice  take  place?  The  formation 
of  neVe  from  snow  is  sometimes  stated  to  be  due 
partly  to  melting  and  recrystallisation  of  part  of  the 
mass,  and  partly  to  pressure  of  overlying  snow,  but 
the  process  does  not  appear  to  be  quite  so  simple. 
The  neve  is  composed  of  grains,  of  which  each  grain 
is  a  truly  crystalline  particle. 

"  Regarded  from  a  distance  the  neVe  appears  to  be  very 
finely  stratified,  layers  of  comparatively  pure  blue  ice 
alternating  with  white  ones.  On  close  examination  this 
stratified  appearance  is  seen  to  be  practically  wholly  due 
to  the  distribution  in  layers  of  countless  imprisoned  air- 
bubbles.  .  .  .  After  a  fall  of  snow  surface-melting  leads 
to  the  production  of  a  mass  of  more  or  less  spherical 
granules  of  ice,  the  interstices  between  which  are  occupied 
by  air.  Further  accumulations  of  snow  lead  to  pressure, 
the  granules  are  compressed,  and  much  of  the  air  may  be 
expelled.  But  under  certain  conditions  of  weather  a 
surface  layer  of  snow  may  be  melted,  and,  freezing  again, 
may  form  an  impervious  layer,  and  the  adjacent  air- 
bubbles  be  unable  to  escape,  even  under  the  pressure 
resulting  from  further  falls  of  snow.  Thus  we  have  bands 
of  air-bubbles  parallel  with  the  surface,  and  alternating 
with  strata  of  blue  ice  which  are  comparatively  free  from 
air.  Meteorological  conditions  will  have  a  great  influence 
upon  the  volume  of  air  imprisoned."1 

match  in  nature  save  the  gentian,  which  expands  its  lovely  flowers 
close  to  the  glacier.  The  sides,  scathed  by  lightning  and  torn  by  the 
avalanche,  scarcely  permit  a  resting-place  for  the  snow  which  accumu- 
lates in  dazzling  wreaths  only  in  its  sheltered  nooks.  Each  of  these 
pinnacles  transported  to  an  ordinary  scene  would  seem  one  of  nature's 
grandest  objects,  whilst  here  it  is  lost  amidst  the  crowd  of  its  fellows." 
1  R.  M.  DEELEY  and  G.  FLETCHER,  "The  Structure  of  Glacier  Ice 
and  its  Bearing  upon  Glacier  Motion,"  Geological  Magazine,  decade  iv., 
vol.  ii.  (1895),  P-  152. 


FROST,   SNOW,   AND    ICE  283 

As  the  neve  passes  into  glacier  ice,  the  stratifica- 
tion is  still  preserved  for  some  distance,  though  the 
bubbles  are  gradually  expelled  owing  to  the  pressure 
by  which  the  ice  is  affected.  The  neve  grains  grow, 
according  to  Hagenbach,  by  the  absorption  of  the 
smaller  grains  by  the  larger  ones,  and  at  the  end  of 
a  glacier  the  grains  may  be  of  very  great  size.  In 
Spitsbergen  "  some  of  them  in  a  block  which  had 
fallen  from  the  Booming  Glacier  were  four  inches  in 
diameter.  These  were  much  bigger  than  any  we  had 
seen  in  Switzerland  ;  and  the  biggest  that  we  re- 
member recorded  thence  were  some  found  by  Forel 
on  the  Aletsch  glacier,  which  were  as  much  as  three 
inches  in  diameter." 1 

Special  attention  is  called  to  the  glacier  grains, 
as  they  produce  a  very  marked  effect  upon  the 
appearance  of  glacier  ice.  The  boundaries  of  the 
grains  in  the  ice  are  usually  extremely  irregular. 
Often  they  are  arranged  in  roughly  parallel  layers 
with  their  longer  axes  parallel  to  the  layers,  and 
we  thus  find  the  peculiar  veined  or  ribboned  structure 
of  glacier  ice,  which  has  been  compared  to  the 
cleavage  structure  of  slates,  and  appears  to  have  been 
produced  in  much  the  same  way  as  the  result  of 
pressure,  producing  a  rearrangement  of  the  particles, 
or  change  of  shape,  accompanied  by  shear,  which 
gives  rise  to  the  lamination,  or,  as  it  might  be  termed, 
cleavage. 

It  does  not  follow  that  because  the  Swiss  glaciers 
are  produced  by  passage  of  snow  into  neve,  and 
of  the  latter  into  glacier  ice,  that  all  glaciers  are  so 

1  E.  J.  GARWOOD  and  J.  W.  GREGORY,  "Contributions  to  the 
Glacial  Geology  of  Spitsbergen,"  Quart.  Journ.  Geo.  Soc.,  vol.  liv., 
p.  220. 


284     SCIENTIFIC   STUDY   OF   SCENERY 

caused.  According  to  Messrs.  Garvvood  and  Gregory1 
"  many  of  the  Spitsbergen  glaciers  do  not  drain 
snow-fields,  and  the  material  of  which  they  consist 
passes  directly  into  the  condition  of  neve-ice  and 
glacier-ice.  Thus  at  the  head  of  nearly  every  glacier 
pass  that  we  crossed  (for  example,  Fox  Pass,  Bolter 
Pass,  Flower  Pass)  we  found  no  true  neve  or  gathering 
ground  for  snow.  In  some  cases  such  glacier-ice 
may  have  been  formed  by  avalanches ;  but  at  least 
in  one  case  this  explanation  is  inadmissible,  and  we 
were  forced  to  the  conclusion  that  under  arctic 
conditions  snow  may  be  converted  into  ice  without 
pressure,  and  that  the  existence  of  glaciers  does  not 
necessarily  postulate  the  existence  of  great  snow- 
fields." 

The  cause  of  movement  of  the  glacier  is  a  topic 
which  has  given  rise  to  much  controversy.  Many 
theories  of  glacier  motion  have  been  suggested,  some 
of  which  assign  gravitation  as  the  primary  cause  of 
the  movement,  while  others  maintain  that  the  cause 
is  heat  The  theories  which  regard  heat  as  of 
primary  importance  are  those  of  Charpentier, 
Agassiz,  Moseley,  and  Croll,  while  those  which  lay 
stress  upon  gravitation  were  enunciated  by  Saussure, 
Rendu,  J.  D.  Forbes,  and  Tyndall.  The  theory  of 
Forbes,  which  regards  ice  as  a  viscous  substance, 
and  therefore  capable  of  movement,  is  the  one  which 
is  generally  accepted  at  the  present  day,  and  without 
entering  into  any  discussion  as  to  the  exact  physical 
conditions  which  constitute  viscosity,  it  is  sufficient 
for  our  purpose  to  note  that  whether  ice  is,  or  is  not, 
strictly  viscous,  in  the  technical  sense  of  the  term,  its 
motion  is  similar  to  that  of  a  viscous  substance. 
1  GARWOOD  and  GREGORY,  loc.  cit.,  p.  200. 


FROST,   SNOW,   AND    ICE  285 

The  movement  of  ice  as  a  viscous  body  does  not, 
of  course,  prevent  the  action  of  thrusting,  and  this 
action  undoubtedly  produces  minor  effects  in  glacier 
movement,  as  shown  by  Garwood  and  Gregory  in  the 
case  of  the  Booming  glacier  of  Spitsbergen. 

A  glacier  then  moves  like  a  river,  and  like  a  river 
its  lower  surface  is  retarded  by  friction  against 
its  bed,  and  accordingly,  as  is  well  known,  owing  to 
accurate  measurements  taken  by  many  observers, 
especially  by  Forbes,  it  moves  faster  at  the  surface 
than  at  the  bottom,  and  faster  in  the  middle  than  at 
the  sides.  Furthermore,  other  things  being  equal,  it 
moves  faster  on  a  steep  incline  than  on  a  gentler 
one. 

Owing  to  the  differential  movement  of  glaciers 
several  phenomena  are  produced,  which  we  may  now 
proceed  to  consider.  In  the  first  place,  in  the  region 
of  neve  the  upper  part  often  adheres  to  the  underlying 
rocks,  while  at  a  lower  elevation,  where  the  frozen 
material  is  thicker,  it  is  capable  of  freer  movement, 
and  is  dragged  away  from  the  more  firmly  attached 
portion,  and  if  the  action  takes  place  so  quickly  that 
the  ice  cannot  adjust  itself  to  the  new  conditions  by 
re- arrangement  of  its  particles  the  lower  part  is 
separated  from  the  higher  by  actual  rupture,  producing 
a  fissure  at  right  angles  to  the  direction  of  pull. 
Such  a  fissure,  which  often  runs  for  a  considerable 
distance  on  the  sides  of  the  higher  peaks,  is  known 
as  a  bergschrund.  The  fissure  is  inclined  inwards 
towards  the  higher  part  of  the  mountain.  It  may 
be  upwards  of  thirty  feet  in  width.  The  bergschrund 
is  often  partially  choked  with  snow,  and  may  have 
cornices,  as  well  as  actual  snow-bridges  in  places, 
and  the  formation  of  icicles,  in  the  manner  previously 


286     SCIENTIFIC   STUDY   OF   SCENERY 

described,  is  peculiarly  favoured  by  the  shaded  state 
of  the  interior  of  the  bergschrund.  Very  often  two 
or  more  of  these  fissures  are  parallel  to  one  another 
at  no  great  distance  apart.  They  are  often  formed 
in  snow-filled  gullies  or  couloirs,  where  the  slope 
suddenly  changes. 

The  fissures  which  are  seen  in  an  ordinary  glacier 
are  known  as  crevasses,  and  are  of  three  kinds,  namely, 
transverse,  longitudinal,  and  marginal.  The  trans- 
verse crevasses  are  produced  when  the  slope  of  the 
glacier  bed  increases  suddenly,  so  that  the  ice  cannot 
accommodate  itself  to  its  bed  without  cracking.  In 
other  words,  transverse  crevasses  are  the  result  of  an 
"  ice-fall,"  analogous  to  the  waterfall  of  a  river.  Such 
crevasses  may  be  seen  at  the  ice-fall  of  the  glacier 
below  the  Scerscen  and  Roseg,  as  shown  in  the  plate. 
The  cracks  are  naturally  at  right  angles  to  the 
direction  of  movement  of  the  ice,  and  accordingly 
they  are  termed  transverse.  The  broken  ice  is 
carried  over  these  steep  portions  slice  after  slice. 
Local  strain  during  the  fall  often  causes  further 
fissuring,  at  an  angle  to  the  main  crevasses,  and 
accordingly  the  ice  may  be  broken  up  into  fantastic 
pinnacles  known  as  se"racs.  Below  the  ice-fall  the 
ice  moves  more  slowly,  and  the  more  quickly  moving 
ice  above  is  jammed  against  it.  Furthermore  the 
ice  over  the  fall  tends  to  take  a  convex  curve  on  the 
surface,  causing  great  tension  of  the  upper  portion, 
while  below  the  surface  becomes  concave,  causing 
compression  of  the  upper  portion.  Owing  to  these 
causes  the  crevasses  formed  at  an  ice-fall  are  sealed 
up  at  no  great  distance  below,  though  they  are  often 
marked  by  superficial  furrows  separated  by  ridges  for 
some  distance  below  the  fall.  It  will  be  seen,  there- 


ROSEG    ENGADINE 


ENGI.ACIAL    RIVKR.   KINGS   GLACIER,  SPITSBERGEN 


FROST,   SNOW,   AND    ICE  287 

fore,  that  though  an  ice-fall  is  constantly  marked 
by  transverse  crevasses,  they  are  not  the  same 
crevasses.  As  one  set  moves  down,  and  gets  sealed 
up,  another  set  is  formed  at  the  fall'  and  takes  its 
place,  and  so  the  process  goes  on.  Below  these  ice- 
falls  the  veined  structure  is  frequently  found,  and 
Tyndall  has  spoken  of  them  as  structure-mills  where 
the  veining  is  produced. 

The  longitudinal  crevasses  occur  where  the  glacier- 
bed  is  somewhat  suddenly  widened  below  a  narrow 
portion.  Tension  is  here  at  right  angles  to  the 
direction  in  which  it  occurred  at  the  ice-fall,  owing 
to  the  inability  of  the  ice  to  adapt  itself  to  its 
widened  bed  without  fissuring. 

Marginal  crevasses  start  at  the  sides  of  the  glacier 
and  extend  towards  the  middle,  pointing  up  the 
glacier  towards  the  middle.  They  are  produced 
owing  to  the  faster  movement  of  the  central  portion 
when  compared  with  that  of  the  sides.  The 
obliquity  of  the  crevasses  was  first  explained  by  Mr. 
W.  Hopkins,  and  a  very  clear  explanation  of  it  will 
be  found  in  Tyndall's  Forms  of  Water,  paragraphs 
267-275.  If  we  imagine  a  circular  portion  of  ice  at 
the  side  of  the  glacier  at  any  time,  that  circle  as  the 
result  of  differential  movement  will  be  converted  into 
an  ellipse,  as  shown  in  Fig.  38,  where  X  X  repre- 
sents the  rocky  side  of  the  glacier;  the  arrow  points 
down  the  glacier;  I  represents  the  original  circle,  and 
2  the  direction  of  inclination  of  the  ellipse  produced 
by  its  distortion.  The  pressure  will  be  greatest  at 
right  angles  to  the  longer  axis  of  the  ellipse,  while 
the  greatest  tension  will  be  at  right  angles  to  the 
direction  of  greatest  pressure,  and  accordingly  the 
fissure  will  be  produced  along  the  direction  of 


288     SCIENTIFIC   STUDY   OF   SCENERY 

the  shorter  diameter  of  the  ellipse  c  d,  which, 
as  will  be  seen  in  the  figure,  points  obliquely 
up  the  glacier  towards  its  centre.  Owing  to  the 
coalescence  of  the  marginal  crevasses  with  trans- 
verse crevasses  in  the  centre  of  the  glacier,  curved 
fissures  are  often  seen,  with  their  convexities  pointing 
up  the  glacier. 

When    glaciers    spread    into    a    fan-like    form    at 


FIG.  38. 

their  extremities,  as  they  sometimes  do,  the  trans- 
verse crevasses  run  in  curves  with  their  convexities 
pointing  downwards,  and  the  longitudinal  ones 
become  radial. 

In  very  cold  regions  there  is  yet  another  way  in 
which  crevasses  may  be  formed.  At  a  very  low 
temperature  ice  changes  its  physical  characters,  and 
becomes  very  inelastic,  and  as  it  contracts  as  the 
result  of  the  lowering  of  the  temperature,  fissures 
may  be  produced.  Mr.  K.  J.  V.  Steenstrup  found 
that  when  ice  was  in  this  condition  the  mere  pressure 
of  a  needle  was  sufficient  to  splinter  off  large  pieces 


FROST,   SNOW,   AND    ICE  289 

of  ice  in  little  fragments,  which  were  thrown  to  some 
distance  with  an  explosive  sound.1 

In  considering  the  formation  of  crevasses  only  the 
differential  movement  of  the  ice  has  been  noticed. 
The  rate  of  movement  of  glaciers  as  a  whole  does 
not  directly  affect  our  present  line  of  inquiry :  it  is 
sufficient  to  state  that  it  varies  in  different  glaciers 
as  well  as  in  different  portions  of  the  same  glacier. 
Some  glaciers  only  move  a  few  inches  per  diem, 
while  in  other  cases  a  rate  of  several  feet  in  a  day 
has  been  recorded. 

In  the  upper  parts  of  the  glaciers,  where  the 
underlying  ice  is  concealed  by  snow,  the  crevasses 
themselves  are  often  concealed,  or  only  revealed  by 
the  presence  of  slight  undulations  noticeable  by  the 
experienced  ice-man.  Further  down  the  glacier  they 
are  open  to  the  light  of  day,  though  often,  like  the 
bergschrund,  crossed  by  snow-bridges ;  while  in  the 
lower  reaches  of  the  ice  we  may  look  down 
unchecked  into  their  blue  depths,  until  they  are  lost 
in  the  gloom  of  the  interior. 

The  fact  that  many  glaciers  descend  below  the 
snow-line  has  already  been  noticed,  and  mentioned 
as  one  of  the  proofs  of  movement  of  a  glacier,  for 
if  the  ice  were  not  replenished  from  behind  it  would 
be  melted  like  the  snow,  and  cease  at  the  snow-line. 
Owing  to  movement  the  process  of  replenishment 
does  go  on,,  for  the  surface  of  the  glacier  is  constantly 
being  lowered  by  melting  or  ablation,  as  it  is  termed, 
and  as  it  nevertheless  often  keeps  the  same  general 
height  for  considerable  periods  of  time,  in  spite  of 
this  ablation,  it  is  perfectly  clear  that  the  com 
pensation  for  the  melted  portion  is  made  by  the 

1  Meddelelser  om  Gronland,  part  vi. 
U 


290    SCIENTIFIC   STUDY   OF   SCENERY 

addition  of  fresh  material  from  the  higher  parts  of 
the  ice-world.  Owing  to  the  heat  received  from  the 
rocks  at  the  side  of  the  glacier,  ablation  takes  place 
more  quickly  at  the  sides  than  towards  the  centre, 
and  accordingly  a  cross  section  of  a  glacier  usually 
presents  a  convex  outline  of  the  surface. 

As  the  result  of  melting,  runnels  and  streams  of 
water  are  often  found  on  the  surface  of  a  glacier, 
especially  on  a  summer  day.  When  traced  down- 
wards they  frequently  disappear,  being  swallowed  by 
the  ice  at  a  crevasse.  Action  takes  place  here  similar 
to  that  described  when  discussing  the  mode  of  forma- 
tion of  swallow-holes  in  a  limestone  district.  The 
water,  often  charged  with  rock-fragments,  falls  down 
the  crevasse  with  a  gyratory  movement  and  wears 
out  a  cylindrical  shaft,  which  may  be  excavated  to 
the  base  of  the  glacier.  These  shafts,  known  as 
moulins,  show  the  beautiful  blue  colour  of  ice,  which 
is  also  exhibited  in  the  crevasses.  As  the  ice  moves 
onwards,  the  crevasse,  as  before  described,  is  sealed 
up,  and  a  fresh  one  formed  in  its  place.  The  old 
moulin  is  now  deserted  by  the  water,  which  excavates 
another  shaft  in  a  place  situated  a  little  higher  up 
the  glacier  than  the  position  now  occupied  by  the 
deserted  one,  and  as  a  result  of  the  continuation  of 
the  process  a  line  of  several  of  these  deserted  moulins 
may  be  found  below  the  position  occupied  by  the 
active  one.  As  a  result  of  ablation  and  other 
changes,  they  gradually  become  shallower,  and  finally 
disappear. 

The  water  which  flows  on  the  surface,  and  is 
swallowed  up  by  crevasses,  ultimately  finds  its  way 
to  the  base  of  the  ice,  though  as  will  be  eventually 
seen,  some  of  it  may  flow  in  the  ice  for  long  distances 


FROST,   SNOW,   AND    ICE  291 

in  englacial  caverns  before  it  finally  reaches  the 
bottom.  This  englacial  and  subglacial  running  water 
issues  from  the  end  of  a  glacier,  often  in  a  con- 
siderable stream,  giving  rise  to  a  terminal  cavern, 
frequently  exhibiting  the  beautiful  blue  colour  of  the 
ice.  It  is  advisable  to  abstain  from  entering  these 
caverns  without  expert  guidance,  as  the  caverns  are 
enlarged  by  the  detachment  of  large  masses  of  ice 
from  the  roof,  often  without  any  preliminary  warning. 

We  have  hitherto  regarded  the  ice  of  glaciers  as 
though  it  flowed  onwards  devoid  of  any  burden, 
though  it  is  well  known  that  much  material  is  carried 
down  by  many  glaciers  in  the  form  of  moraines, 
and  we  may  now  proceed  to  consider  the  character 
and  mode  of  distribution  of  this  material  on  and  in 
the  ice. 

The  action  of  frost  in  splitting  fragments  from 
the  solid  rocks  has  already  been  noticed,  and  it  was 
seen  that  these  fragments,  when  the  slope  is  steep, 
roll  down  the  hill-sides  to  the  valley  beneath.  If  the 
bottom  of  that  valley  is  occupied  by  a  glacier  many 
of  these  stones  will  come  to  rest  on  the  side  of  the 
glacier,  retaining  the  angular  shape  which  they 
possessed  when  split  from  the  parent  rock.  The 
angular  fragments  will  descend  upon  some  parts 
of  the  glacier  more  frequently  than  on  others,  the 
greatest  number  falling  down  gullies  which  are 
spoken  of  as  screes-shoots.  But  as  the  glacier 
moves  along,  each  portion  of  the  side  in  turn  passes 
such  a  screes-shoot,  and  the  material  which  is  piled 
upon  it  there  is  carried  lower  down,  while  the  process 
is  going  on  afresh  at  the  original  place.  Accordingly 
every  part  of  the  glacier  side  becomes  fringed  with 
an  accumulation  of  loose  blocks,  giving  rise  to  a 


292     SCIENTIFIC   STUDY   OF   SCENERY 

lateral  moraine  upon  either  side  of  the  ice-river. 
When  two  tributary  glaciers  unite  to  form  a  single 
ice-stream,  the  adjacent  lateral  moraines  also  unite, 
and  proceed  down  the  centre  of  the  main  stream, 
thus  producing  a  medial  moraine,  and  when  a  glacier, 
as  in  the  case  of  the  Mer  de  Glace  at  Chamonix, 
is  formed  by  the  union  of  many  tributaries,  a  number 
of  medial  moraines  occupy  the  central  portions  of 
its  surface.  Now  a  glacier,  like  a  river,  tends  to 
continue  in  its  initial  course,  and  when  a  bend  occurs 
in  its  bed,  the  line  of  most  rapid  motion  is  diverted 
from  the  centre  of  the  glacier  towards  the  concave 
curve,  and  the  medial  moraine  is  carried  with  it. 
Consequently,  when  a  glacier  flows  through  a  sinuous 
valley,  the  sinuosities  of  the  medial  moraines  are 
greater  than  those  of  the  actual  valley,  and  the 
peculiar  serpentine  appearance  of  the  moraines  is 
emphasized. 

The  moraines  on  a  glacier  appear  to  consist  of 
great  ridges  composed  of  detritus,  rising  high  above 
the  general  level  of  the  ice.  This  appearance  is 
deceptive  ;  the  stones  form  a  mere  veneer  upon  the 
surface  of  a  ridge  of  ice,  the  icy  ridge  being  due 
to  slighter  ablation  of  the  ice-surface  beneath  the 
moraine,  for  as  rock  is  a  bad  conductor  of  heat,  the 
ice  beneath  the  moraine  is  protected  from  the  rays  of 
the  sun. 

The  formation  of  this  ridge  may  go  on  to  so  great 
an  extent  that  the  slope  becomes  too  steep  for  the 
stones  to  rest  on  it,  when  they  fall  to  either  side,  and 
as  this  process  goes  on  the  original  ice-ridge  may  be 
melted,  and  replaced  by  a  ridge  on  either  side,  which 
may  undergo  the  same  process.  In  this  way  the 
morainic  material  tends  to  wander  laterally  over  the 


FROST,  SNOW,   AND   ICE  293 

glacier,  and  the  lower  portions  of  glaciers  are  thus 
frequently  covered  with  a  mass  of  morainic  matter 
which  may  entirely  conceal  the  ice  beneath. 

When  a  glacier  shrinks  for  many  years  in  succession, 
as  is  the  case  with  many  Swiss  glaciers,  its  general 
level  is  lowered,  and  the  former  height  of  the  ice 
is  marked  by  the  original  lateral  moraines,  while  a 
continuous  slope  at  the  angle  of  rest  of  the  loose 
material  formed  of  the  morainic  material  which  was 
stranded  during  the  sinking  of  the  ice-surface 
stretches  from  the  top  of  the  old  moraine  to  the 
present  level  of  the  glacier,  which  may  be  some 
hundreds  of  feet  beneath  it. 

The  medial  moraines  are  sometimes  engulfed  by 
crevasses,  and  then  reappear  at  some  distance  from 
the  place  where  they  were  engulfed,  owing  to  the 
ablation  of  the  surface. 

A  certain  amount  of  material,  such  as  stones,  sand, 
and  very  fine  mud  is  carried  beneath  the  ice,  consti- 
tuting the  moraine  prof onde ;  it  is  chiefly  of  interest 
to  us  on  account  of  the  effect  it  produces  on  the 
underlying  rocks,  which  will  be  noticed  in  a  later 
chapter. 

At  the  termination  of  the  glacier  all  the  rocky 
material  which  has  been  transported  by  the  ice, 
whether  on  its  surface,  in  its  substance,  or  beneath 
it,  is  deposited  to  form  a  terminal  moraine.  As  the 
centre  of  the  glacier,  owing  to  its  more  rapid  move- 
ment, is  carried  further  down  than  the  sides  before 
it  melts,  the  termination  of  the  glacier  is  often  con- 
vex, with  the  convexity  of  the  curve  pointing  down 
the  valley.  Accordingly  the  terminal  moraine  tends 
to  assume  a  crescentic  form,  and  if  a  glacier  recedes, 
and  there  are  pauses  in  the  recession,  a  considerable 


294    SCIENTIFIC   STUDY,  OF  SCENERY 

quantity  of  material  accumulates  at  the  end  during 
each  of  the  pauses,  and  a  number  of  crescents 
of  morainic  material  may  be  formed  one  behind 
another. 

The  stream  which  issues  from  the  glacier,  and  the 
streamlets  which  course  down  the  valley  sides,  often 
issuing  from  the  ends  of  minor  glaciers,  cause  much 
re-sorting  of  the  morainic  material,  often  filling  up 
inequalities  of  the  valley,  and  giving  rise  to  a  fairly 
uniform  surface  of  fluvio-glacial  deposit,  which  occurs 
below  the  ends  of  many  of  the  Alpine  glaciers,  while 
ancient  fluvio  -  glacial  deposits  laid  down  during 
former  extension  of  the  ice,  and  subsequently  de- 
nuded in  the  centre  by  the  river,  form  shelves  on 
the  valley  sides,  frequently  covered  with  a  rich  soil, 
and  accounting  for  the  presence  of  many  of  the 
Alpine  pastures  at  considerable  heights  above  the 
present  valley  bottoms. 

Owing  to  the  surface -wandering  of  morainic 
material,  and  other  causes,  detached  fragments  are 
often  found  on  the  ice,  which  may  be  of  any  size 
from  blocks  the  size  of  a  cottage  down  to  the  finest 
particles  of  mud.  The  large  blocks,  like  the  moraines, 
protect  the  ice  beneath  from  the  sun's  rays.  Accord- 
ingly a  large  block  is  often  found  standing  on  a 
pinnacle  of  ice,  produced  owing  to  this  protective 
action,  forming  what  is  known  as  a  glacier-table. 
This  resembles  to  some  extent  the  earth-pillars 
of  which  we  have  before  spoken,  and  still  more 
certain  boulders  which  are  sometimes  found  perched 
upon  pinnacles  of  limestone  which  they  have  pro- 
tected from  solution,  as  the  celebrated  blocks  of 
slate  which  rest  on  pinnacles  of  the  mountain  lime- 
stone at  Norber,  near  Settle,  Yorkshire.  As  the 


FROST,   SNOW,   AND    ICE  295 

pinnacles  of  ice  increase  in  height  the  sun  gradually 
diminishes  their  thickness,  and  in  the  Alps,  the  rays 
being  most  powerful  on  the  south  side,  the  pinnacle 
is  melted  away  more  rapidly  on  that  side,  and  the 
superincumbent  capping-stone  gradually  acquires  a 
slant  towards  the  south,  when  it  slips  off,  and  a  new 
table  is  formed,  while  the  original  pinnacle  of  ice 
may  remain  to  the  north  of  it  for  some  time,  though 
it  is  eventually  melted. 

Little  collections  of  stone  produce  the  same  effect, 
giving  rise  to  cones  of  ice,  such  as  are  frequent  upon 
parts  of  the  Corner  Glacier.  The  stones  slip  from 
these,  as  they  do  from  moraines,  when  the  slope  of 
the  cone  has  become  too  great.  In  parts  of  Green- 
land cones  of  this  character  occur  with  a  height  of 
sixty  feet. 

When  the  particles  are  small  a  different  effect  is 
produced.  Rock,  though  a  bad  conductor,  is  a  good 
absorber  of  heat,  and  as  these  small  particles  are 
thin  the  absorbed  heat  is  partly  conducted  through 
them  and  melts  the  ice  beneath,  and  accordingly 
small  particles  of  stone  gradually  bore  their  way 
down  into  the  ice,  leaving  a  little  pool  of  water 
above,  and  when  they  are  abundant  they  produce 
a  very  noticeable  honeycombed  appearance  of  the 
surface  of  the  glacier. 

Lastly,  we  must  notice  the  well-known  dirt-bands 
of  glaciers,  first  observed  by  Forbes  on  the  Mer  de 
Glace,  which  give  such  clear  indication  of  glacier 
movement.  They  originate  below  an  ice-fall,  where 
the  crevasses,  though  sealed  up,  give  rise  to  alternate 
transverse  ridges  and  furrows  on  the  surface  of  the 
ice.  Dirt  is  carried  by  wind  and  streamlets  into 
the  furrows,  and  as  the  ice  moves  onwards  the  ridges 


296    SCIENTIFIC   STUDY   OF   SCENERY 

disappear  by  ablation,  but  the  dirt  which  has  been 
swept  into  the  furrows  still  remains,  and  owing  to 
the  more  rapid  movement  of  the  central  part  of  the 
ice,  assumes  the  familiar  curved  appearance,  the 
convexities  of  the  curves  pointing  down  the  glacier. 
The  phenomena  which  have  been  described  in  the 
present  chapter  may  all  be  studied  in  the  Alpine 
regions  of  Switzerland,  but  there  are  many  other 
glaciated  areas  which  present  scenic  features  of 
interest,  sometimes  of  a  different  kind  from  those 
occurring  in  Switzerland,  sometimes  similar  in  kind, 
but  on  a  larger  scale.  It  will  be  convenient  to 
consider  these,  by  a  cursory  examination  of  some 
of  the  other  glaciated  regions  of  the  world,  and  to 
this  we  may  devote  another  chapter. 


CHAPTER   XVII. 

GLACIERS   AND    ICE-SHEETS   OF  VARIOUS 
REGIONS 

J\T  OR  WA  Y.— The  glaciers  of  Norway  form  the 
subject  of  a  special  work  by  the  late  J.  D. 
Forbes,1  who  states  that  their  conditions  and  struc- 
ture are  almost  identical  with  those  of  Switzerland, 
the  main  difference  being  the  nature  of  the  gather- 
ing ground  for  the  snows.  In  Switzerland  the  snow 
collects  at  the  heads  of  valleys,  and  by  accumulatidh 
forms  glaciers,  while  in  Norway  it  forms  on  vast 
table-lands  surrounded  by  mountain  peaks,  and  the 
glaciers  escape  through  the  passes  which  form  the 
notches  to  this  mountainous  ring  surrounding  each 
snowy  plateau  ;  accordingly  the  Norwegian  glaciers 
are  smaller  as  compared  with  their  snowfields  than 
are  those  of  Switzerland. 

A  very  beautiful  glacier  in  Fjaerland,  the  Suphelle 
Brae,  is  a  good  example  of  a  type  of  glacier  which 
is  also  found  in  Switzerland,  though  not  in  so  perfect 
a  degree  as  in  the  present  case.  It  is  known  as  a 
renianie  glacier,  and  is  not  connected  with  the  snow- 
field,  but  is  formed  by  the  reconsolidation  of  masses 
of  ice  precipitated  as  avalanches  from  a  glacier  above. 
A  figure  of  it  will  be  found  on  Plate  VII.  of  Forbes' 
work. 

1  FORBES,  J.  D. ,  No-way  and  its  Glaciers  visited  in  1851.  Edinburgh, 

1853. 

297 


298     SCIENTIFIC   STUDY   OF   SCENERY 

Spitsbergen.  —  An  interesting  paper  by  Messrs. 
Garwood  and  Gregory  on  the  glacial  geology  of 
Spitsbergen,  to  which  reference  was  made  in  the 
last  chapter,  gives  some  details  concerning  the  ice 
of  that  region  which  are  of  interest  to  the  student 
of  scenery.  Some  of  the  Spitsbergen  glaciers  are  of 
the  Alpine  type,1  others  present  examples  of  what 
is  known  as  the  piedmont  type,  which  will  be  more 
fully  noticed  when  we  consider  the  nature  of  some 
of  the  Alaskan  glaciers,  while  others  are  composed 
of  a  series  of  confluent  glaciers,  for  which  the  authors 
adopt  the  name  "  inland  ice-sheet,"  which  has  been 
used  in  another  sense  for  the  great  icy  pall  which 
covers  the  interior  of  Greenland,  which,  however,  they 
prefer  to  speak  of  as  an  "  ice-cap." 
_,  The  most  interesting  feature  of  many  of  the  Spits- 
bergen glaciers  is  the  nature  of  the  termination  or 
snout. 

The  ordinary  Alpine  glacier  ends  in  a  tapering 
snout  curving  somewhat  gently  down  to  the  base, 
and  though  this  is  found  in  the  case  of  some  of 
the  glaciers  of  Spitsbergen,  many  of  them  end  in 
a  vertical  face  of  ice,  forming  what  is  known  as  a 
"  Chinese  wall,"  and  having  an  overhanging  cornice 
at  the  top.  The  authors  give  reasons  for  supposing 
that  this  is  due  to  advancing  ice,  and  that  receding 
glaciers  have  the  characteristic  Alpine  termination. 
The  two  kinds  of  ends  are  seen  close  together  in 

1  The  Alpine  glaciers,  of  course,  differ  from  one  another  in  detail, 
and  have  been  spoken  of  as  belonging  to  the  first  and  second  orders. 
There  is  no  essential  difference  between  them  except  that  due  to  size 
and  sometimes  to  inclination  of  slope,  but  there  is  a  marked  contrast 
between  the  large  valley  glaciers  and  the  small  glaciers  adherent  to  the 
slopes  and  faces  of  mountains — hanging  glaciers,  as  the  latter  are 
termed. 


GLACIERS   AND    ICE-SHEETS        299 

the  case  of  the  Booming  and  Baldhead  Glaciers. 
(See  the  plate.)  Baldhead  Glacier  on  the  left  of  the 
plate  shows  the  tapering  snout,  while  Booming 
Glacier  has  a  Chinese  wall.  Some  of  the  advancing 
glaciers  have  beneath  the  vertical  face  a  talus  of 
fallen  blocks,  due  to  the  more  rapid  advance  of  the 
upper  part  of  the  ice,  and  the  authors  show  that 
the  upper  ice  moves  over  the  talus,  which  becomes 
incorporated  in  the  lower  part  of  the  glacier ;  this 
movement,  owing  to  thrusting  action,  produces 
planes  of  discontinuity,  and  so  "  the  glacier  advances 
by  an  'over-rolling'  motion,  the  top  layer  falling 
to  the  bottom,  and  then  working  upward  over  other 
fallen  masses."  They  further  note  that  though  the 
lower  part  of  the  Booming  Glacier  is  advancing,  it 
is  diminishing  near  its  source,  "apparently  owing 
to  a  diminution  of  the  snowfall  at  its  head."  Now 
the  upper  surface  of  this  glacier  is  saucer-shaped, 
having  a  concave  cross-section  in  place  of  the  normal 
convex  one,  and  the  authors  believe  that  this  shape 
is  due  to  subsidence,  "owing  to  the  melting  and 
solution  of  the  lower  layers  of  the  ice." 

Many  of  the  Spitsbergen  glaciers  reach  the  sea 
and  give  rise  to  icebergs,  as  for  instance  King's  Bay 
Glacier,  represented  in  the  frontispiece,  from  a  photo- 
graph by  Mr.  Garwood.  The  origin  of  these  icebergs 
will  be  considered  when  we  discuss  the  nature  of  the 
Greenland  ice-cap. 

Messrs.  Garwood  and  Gregory  also  notice  the 
effect  of  marine  ice  as  an  agent  of  denudation. 
The  effect  of  land  ice  in  this  connection  will  be 
considered  in  the  next  chapter,  but  it  may  be  re- 
marked here  that  as  a  means  of  polishing  and 
striating  rocks,  the  authors  saw  no  means  of  dis- 


300    SCIENTIFIC   STUDY   OF  SCENERY 

criminating  between  the  effects  of  glaciers  and  those 
of  floating  ice. 

Baron  Nordenskjold  describes  some  remarkable 
features  on  the  inland  ice  of  North  East  Land,  which 
are  termed  glacier-canals.  They  have  a  depth  of 
forty  feet  in  places,  a  breadth  of  from  30  to 
loo  feet,  and  mostly  run  parallel  to  one  another, 
with  an  interval  of  300  feet  only  between  adjoining 
canals  in  places.  The  walls  are  very  straight  and 
steep.  Nordenskjold  suggests  that  they  are  pro- 
duced by  faulting  of  the  ice,  due  to  alternate 
contraction  and  expansion  of  the  ice  owing  to 
changes  of  temperature.1 

Alaska. — Some  of  the  Alaskan  glaciers  are  of  the 
piedmont  type,  and  have  been  described  by  Messrs. 
I.  C.  Russell  and  H.  P.  Gushing.2  The  Muir  Glacier, 
described  by  Gushing,  lies  east  of  Mount  Fairweather, 
and  ends  in  the  Muir  Inlet  of  the  Pacific  Ocean. 
It  lies  in  an  amphitheatre,  partly  surrounded  by  a 
semicircle  of  mountains,  from  which  icy  tributary 
glaciers  of  the  Alpine  type  pour,  and  give  rise  to  a 
great  mass  of  nearly  inert  ice— the  piedmont  glacier — 
having  a  breadth  of  from  twelve  to  over  fifteen  miles. 
As  it  approaches  the  inlet  it  is  narrowed,  and  the  ice 
is  forced  through  a  gap  less  than  three  miles  wide. 
The  inert  ice  is  slowly  rotting  where  it  lies,  and  is 
extremely  smooth.  Some  of  the  tributaries  are  also 
inert ;  for  instance,  the  Dirt  Glacier,  the  lower  part 
of  which  is  completely  covered  with  debris.  Two 
valleys,  namely,  Main  Valley  and  Berg  Valley, 

1  The    Arctic    Voyages   of  Adolf  Erik   Nordenskjold,    1858-1879; 
London,    1879,  P-  25&>  and  figure  on  p.  259. 

2  RUSSELL,  I.  C.,  Thirteenth  Annual  Report  of  the  U.S.   Geological 
Survey,  and  GUSHING,  H.  P.,  American  Geologist,  1891. 


GLACIERS    AND    ICE-SHEETS         301 

contain  ice  in  an  extremely  remarkable  state,  perhaps 
foreshadowed  by  the  upper  part  of  Booming  Glacier 
in  Spitsbergen.  The  glaciers  occupying  these  valleys 
are  retreating  at  the  heads  instead  of  at  the  snouts 
of  the  ice,  the  ice  of  Main  Valley  terminating  ab- 
ruptly, and  holding  up  the  waters  of  a  lake  which 
occupies  the  head  of  the  valley  (as  noticed  in 
Chapter  XL),  though  Mount  Young,  the  highest 
mountain  in  the  immediate  vicinity,  dominates  the 
valley  head.  Similarly  the  glacier  in  Berg  Valley 
holds  up  the  waters  of  Berg  Lake.  The  medial 
moraines  of  these  glaciers  stretch  right  up  to  the 
ice-cliffs  overlooking  the  lakes,  and  there  is  therefore 
no  doubt  that  the  ice  once  extended  upwards  and 
has  retreated  from  the  valley  heads. 

The  Malaspina  Glacier,  described  by  Russell,  is 
also  a  piedmont  glacier,  supplied  by  tributaries 
descending  from  the  Mount  St.  Elias  range.  The 
average  length  of  the  glacier  is  from  twenty  to 
twenty-five  miles,  but  it  has  a  breadth  of  about 
seventy  miles  and  an  approximate  area  of  1500 
square  miles.  It  consists  of  a  nearly  horizontal 
plateau  of  ice,  the  central  portion  being  free  from 
moraines  and  deeply  crevassed,  and  having  a  broadly 
undulating  surface.  It  possesses  three  principal 
lobes,  each  being  a  piedmont  expansion  of  a  large 
tributary  glacier,  and  the  lobes  are  separated  by 
medial  moraines.  Part  of  the  ice  reaches  the  sea 
and  forms  icy  cliffs,  from  which  bergs  break  off, 
but  other  parts  are  separated  from  the  ocean  by 
a  plain  covered  by  glacio-marine,  fluvio-glacial,  and 
glacial  deposits,  occupied  by  dense  forests,  and  pitted 
with  morainic  lakes. 

The  end  of  the  Malaspina  Glacier  is  largely  covered 


302     SCIENTIFIC   STUDY   OF   SCENERY 

with  debris,  due  to  spreading  of  morainic  material  in 
the  way  previously  described,  and  also  to  ablation. 
Some  parts  of  this  moraine-covered  portion  of  the 
glacier  are  clothed  with  dense  forests  and  under- 
growth of  alder,  spruce,  huckleberry,  ferns,  etc.  It 
is  only  on  the  inert  or  stagnant  ice  that  these  forests 
grow.  They  extend  in  places  to  a  distance  of  four 
to  five  miles  from  the  edge  of  the  ice,  and  in  many 
places  the  ice  below  them  is  not  less  than  1000  feet 
thick. 

The  inert,  and  partly  inert  ice  of  this  glacier  is 
drained  by  an  extensive  system  of  englacial  rivers, 
forming  caverns  in  the  ice,  which  sometimes  become 
choked  with  debris,  an  occurrence  of  considerable 
importance  to  the  geologist.  As  the  ice  melts  on  the 
surface,  portions  of  these  caverns  may  be  exposed, 
while  intermediate  portions  are  still  arched  over, 
showing  tunnels  of  ice. 

Mr.  Garwood  has  subsequently  observed  these  en- 
glacial  rivers  on  the  ice  of  Spitsbergen,  and  I  am 
able  to  give  a  reproduction  of  a  photograph  of  one 
of  these  in  the  accompanying  plate. 

It  is  interesting  to  notice  that  since  glaciation 
commenced  in  the  region,  earth  movement,  accom- 
panied by  faulting,  has  occurred  to  such  an  extent  as 
to  raise  portions  of  the  glacio-marine  deposits  to  a 
height  of  over  2000  feet  above  sea-level.  These 
elevated  parts  (the  Chaix  Hills)  projecting  through 
the  ice,  furnish  admirable  illustrations  of  the  typical 
mountain  forms  produced  by  the  erosion  of  running 
water. 

Greenland. — The  great  surface  of  inland  ice  of 
Greenland,  long  known  in  a  general  way,  has  been 
more  carefully  studied  of  recent  years  by  Torell, 


GLACIERS   AND    ICE-SHEETS         303 

Nordenskjold,  Nansen,  Chamberlain,  Peary,  and 
Drygalski,  among  others ;  but  a  systematic  explora- 
tion has  been  undertaken  by  a  Danish  Commission, 
and  the  results  published  in  a  valuable  series  of  re- 
ports, entitled  Meddelelser  om  Gronland,  from  which 
most  of  the  following  account  is  abstracted. 

The  inland  ice  or  ice-cap  of  Greenland  is  estimated 
to  occupy  an  area  of  about  20,000  square  miles.  It 
appears  to  form  a  gently  sloping  plateau,  the  in- 
clination of  which,  away  from  the  coast,  seldom 
exceeds  i°  for  any  distance,  so  that  the  surface 
usually  appears  as  a  plain,  as  is  well  shown  by  Dr. 
Nansen's  transverse  section,  drawn  to  true  scale 
between  Umivik  and  Ameralik  Fjords.  (See  plate 
at  end  of  volume  ii.  of  The  First  Crossing  of  Green- 
land^) 

As  is  well  known,  no  rocky  "divide"  marks  the 
centre  of  the  country  along  the  line  of  traverse  taken 
by  Nansen  ;  on  the  contrary,  nothing  but  snow  and 
ice  was  seen  after  leaving  the  rocks  of  one  coast 
until  those  of  the  other  were  sighted,  and  the  extreme 
purity  of  the  surface  of  the  ice  in  other  places  where 
it  has  been  explored  leads  one  to  suppose  that  a 
rocky  "  divide  "  is  absent  elsewhere.  Next  to  extent 
of  ice,  the  absence  of  superficial  morainic  material  on 
the  Greenland  ice  (save  under  exceptional  circum- 
stances to  be  noted  presently)  forms  the  great 
contrast  between  it  and  that  of  the  glaciers  of  a 
country  like  Switzerland.  The  surface  of  the  ice 
is  also  in  many  places  free  from  crevasses  for  con- 
siderable distances,  and  accordingly  the  superficial 
rivers  of  the  Greenland  inland  ice  often  attain  a  great 
size  and  volume,  and  when  they  do  form  moulins 
these  are  of  exceptional  magnificence.  Here  is  a 


304     SCIENTIFIC   STUDY   OF   SCENERY 

description  of  this  superficial  drainage  from  Baron 
Nordenskjold's  pen.1 

"  At  a  short  distance  from  our  turning-point  we  came  to 
a  large,  deep,  and  broad  river  flowing  rapidly  between  its 
blue  banks  of  ice,  which  here  were  not  discoloured  by  any 
gravel,  and  which  could  not  be  crossed  without  a  bridge. 
As  it  cut  off  our  return,  we  were  at  first  somewhat  dis- 
concerted ;  but  we  soon  concluded  that  ...  it  must  at  no 
great  distance  disappear  under  the  ice.  We  therefore  pro- 
ceeded along  its  bank  in  the  direction  of  the  current,  and 
before  long  a  distant  roar  indicated  that  our  conjecture  was 
right.  The  whole  immense  mass  of  water  here  rushed 
down  a  perpendicular  cleft  into  the  depths  below.  We 
observed  another  smaller,  but  nevertheless  very  remarkable 
waterfall  the  next  day.  .  .  .  We  saw,  in  fact,  a  pillar  of 
watery  vapour  rising  from  the  ice  at  some  distance  from 
our  resting-place,  and,  as  the  spot  was  not  far  out  of  our 
way,  we  steered  our  course  by  it  in  the  hope  of  finding — 
judging  from  the  height  of  the  misty  pillar  —  a  waterfall 
still  greater  than  that  just  described.  We  were  mistaken  ; 
only  a  smaller  yet  tolerably  large  river  rushed  down  from 
the  azure-blue  cliffs  to  a  depth  from  which  no  splashes  re- 
bounded to  the  mouth  of  the  fall ;  but  there  arose  instead, 
from  another  smaller  hole  in  the  ice,  in  the  immediate 
vicinity,  an  intermediate  jet  of  water  mixed  with  air,  which, 
carried  hither  and  thither  by  the  wind,  wetted  the  surround- 
ing ice-cliffs  with  its  spray.  We  had  thus  here,  in  the 
midst  of  the  desert  of  inland-ice,  a  fountain,  as  far  as  we 
could  judge  by  the  descriptions,  very  like  the  geysers  which 
in  Iceland  are  produced  by  volcanic  heat." 

On  this  expedition  Nordenskjold  discovered  a  dust 
of  volcanic  material  on  the  surface  of  the  ice,  ac- 
companied by  a  brown  polycellular  alga  and  other 

1  NORDENSKJOLD,  A.  E.,  loc.  cit.,  p.  167. 


GLACIERS    AND    ICE-SHEETS         305 

microscopic  organisms.  The  powder,  which  he  called 
kryokonite,  and  the  accompanying  organisms  form 
"  a  most  dangerous  enemy  to  the  mass  of  ice,"  owing 
to  the  part  which  they  play  on  the  surface-melting. 
"  This  plant  (the  alga)  has  no  doubt  played  the  same 
part  in  our  country;  and  we  have  it  to  thank,  perhaps, 
that  the  deserts  of  ice  which  formerly  covered  the 
whole  of  Northern  Europe  and  America  have  now 
given  place  to  shady  woods  and  undulating  corn- 
fields." 

Towards  the  coast  the  mountains  gradually  appear 
above  the  ice,  first  as  islets  of  rock  (nunataks)  pro- 
jecting through  the  icy  surface,  lastly  as  con- 
tinuous ridges  separating  the  fjords,  into  which  the 
ice  is  finally  discharged,  as  tongues  which  become 
greatly  fissured,  broken  up,  and  finally  carried  away 
as  icebergs.  The  ice  towards  its  termination  is  often 
fairly  steep,  though  even  then  usually  gently  inclined 
as  compared  with  the  surfaces  of  many  Swiss  glaciers. 
In  the  region  of  nunataks  the  surface  of  the  ice  is 
much  fissured  by  transverse  and  longitudinal  cre- 
vasses, depending,  like  the  crevasses  of  Swiss  glaciers, 
on  inequalities  of  the  bed  of  the  ice ;  and  where  the 
ice  can  move  in  fan-shape,  as  in  the  case  of  the 
tongue  known  as  the  Frederikshaab  Glacier,  the 
crevasses  are  radial  and  tangential.  Many  very 
striking  coloured  illustrations  of  the  Greenland 
crevasses  are  given  in  various  numbers  of  the 
Meddelelser. 

Of  the  various  nunataks  which  have  been  described 
the  most  interesting  are  those  of  Jensen,  situated 
about  forty-five  miles  inland,  to  the  east  of  the 
Frederikshaab  Glacier.  They  form  the  summits  of 
mountains  having  a  height  of  about  5000  feet  above 
x 


306     SCIENTIFIC   STUDY    OF   SCENERY 

sea-level,  and  as  the  ice  here  is  nearly  as  high,  only 
the  summits  project.  It  is  of  interest  to  note  that 
even  these  isolated  pinnacles  are  partly  clothed  with 
a  characteristic  arctic  vegetation,  twenty-six  species 
of  plants  having  been  found  upon  them,  including 
Oxyria  renformis^  Saxifraga  oppositifolia.  S.  cernua, 
S.  nivalis,  Papaver  nudicaule,  Draba  alpina,  Silene 
acautis,  Cerastium  alpinum  var.  lanatum,  and  Poten- 
tilla  nivea. 

The  ice  is  piled  up  on  the  inland  side  of  the 
nunataks,  like  water  on  the  higher  side  of  a  stone 
projecting  above  a  river-surface,  and  a  current  of  ice 
sweeps  round  each  side  of  the  rocky  barrier,  some- 
times leaving  a  hollow  below  the  barrier,  which 
becomes  filled  with  water,  giving  rise  to  a  lake. 
Small  tongues  of  ice  are  forced  through  the  passes 
or  cols  between  adjacent  nunataks,  and  end  on  the 
ice  below.  At  the  junction  moraines  are  found,  often 
showing  a  crescentic  outline  (as  well  seen  in  the 
nunataks  of  Dalager,  not  far  from  those  of  Jensen, 
but  nearer  the  coast).  These  moraines  are  of  interest 
on  account  of  the  general  freedom  of  the  Greenland 
ice  from  moraine  material,  but  also  because  their 
character  shows  that  they  are  portions  of  the  moraine 
profonde  brought  to  the  surface  in  exceptional  cir- 
cumstances. 

In  some  of  the  Greenland  ice-masses,  as  well  as  in 
those  of  Spitsbergen,  stratified  material  is  enclosed 
in  the  ice,  and,  owing  to  the  differential  movement 
of  the  ice,  becomes  faulted  and  also  folded  in  a 
remarkable  way,  sometimes  recalling  the  bands  of  an 
agate,  as  shown  at  the  termination  of  the  Njarartor- 
suak  glacier  in  the  fjord  of  Umanak,  figured  in 
Plate  III.  of  the  Fourth  Part  of  the  Meddelelser. 


GLACIERS   AND    ICE-SHEETS         307 

Where  the  Greenland  ice  does  not  reach  the  sea, 
but  terminates  on  low  ground,  the  country  between  it 
and  the  sea  often  consists  of  a  plain  of  fluvio-glacial 
deposits,  presenting  an  extremely  dreary  aspect,  a 
remark  which  may  also  be  made  of  similarly  formed 
plains  in  Spitsbergen.  At  other  times  the  plains  are 
due  to  accumulation  of  glacio-marine  deposits,  as,  for 
instance,  a  portion  of  that  traversed  by  Nansen  at 
the  head  of  the  Ameralik  Fjord  after  he  had  de- 
scended from  the  inland  ice  at  the  conclusion  of  his 
adventurous  journey  across  Greenland. 

We  may  here  discuss  the  mode  of  formation  of  ice- 
bergs, which  break  off  glaciers  in  many  places  where 
the  latter  reach  the  sea,  as  off  parts  of  the  Malaspina 
Glacier,  off  many  of  the  Spitsbergen  glaciers,  as  shown 
in  Garwood's  photograph  of  King's  Bay  Glacier  (see 
frontispiece),  and  especially  off  the  tongues  of  ice 
which  project  into  the  Greenland  fjords. 

It  is  now  unquestionable  that  the  fracture  of  the 
ice  to  form  icebergs  does  not  always  take  place 
owing  to  the  same  causes.  In  some  cases,  when 
the  glaciers  are  terminated  by  a  vertical  face,  fracture 
of  the  emerged  part  of  the  ice  occurs,  and  gives  rise 
to  small  icebergs,  which  fall  with  a  splash  into  the 
water.  In  other  cases,  however,  as  in  the  ice  of 
Jacobshavn  Fjord,  owing  to  the  buoyancy  of  the  ice, 
the  ice  of  the  central  parts  of  the  glacier  floats  on 
the  water,  and  gradually  becomes  broken  up  along 
lines  of  crevasses,  giving  rise  to  a  great  quantity  of 
icebergs.  Some  of  the  bergs  of  Jacobshavn  Fjord 
were  measured  by  Hammer.  The  highest  was  about 
350  feet  above  sea-level,  or  more  than  150  feet  higher 
than  the  upper  edge  of  the  glacier  where  it  reaches 
the  sea.  Others  were  about  half  this  height. 


308     SCIENTIFIC   STUDY   OF   SCENERY 

It  is  well  known  that  when  the  berg  is  in  a  state 
of  stable  equilibrium,  by  far  the  greater  part  of  its 
mass  is  below  the  level  of  the  water.  The  proportion 
of  the  submerged  part  to  that  above  sea-level  differs 
according  to  the  nature  of  the  water,  whether  it  is 
salt  or  fresh,  and  according  also  to  the  character  of 
the  ice.  The  proportion  of  emerged  and  submerged 
ice  in  the  case  of  frozen  sea-water  floating  in  sea- 
water,  is  about  i  :  5'3,  but  that  of  glacier-ice  in 
sea-water  is  approximately  I  :  9.  Accordingly  ice- 
bergs may  easily  be  stranded  on  shoals,  even  where 
the  water  is  of  some  depth,  hence  the  mass  of  icebergs 
which  are  often  found  stranded  on  the  banks  of 
Newfoundland,  and  on  the  shoal  water  which  exists 
between  the  east  coast  of  Greenland  and  Iceland. 

The  submerged  parts  of  bergs  melt  much  more 
rapidly  than  the  emerged  portions,  and  accordingly 
icebergs  frequently  capsize  after  the  submerged  part 
has  been  considerably  melted.  As  the  melting  often 
takes  place  in  an  apparently  capricious  manner,  this 
partly  accounts  for  the  fantastic  forms  which  are 
often  assumed  by  icebergs. 

Huge  as  are  the  icebergs  produced  by  the  'calving' 
of  the  Greenland  ice-tongues,  they  are  far  exceeded 
in  size  by  the  great  tabular  icebergs  which  are  shed 
from  the  almost  unknown  ice-cap  of  the  Antarctic 
regions,  one  of  which  has  been  recorded  with  a 
circumference  of  two  miles. 

We  may  conclude  this  chapter  with  a  few  remarks 
upon  the  colour  of  snow  and  ice.  The  white 
appearance  of  snow,  and  of  rough  ice,  is  due  to 
reflection  of  the  sun  from  innumerable  surfaces,  and 
pure  transparent  ice,  like  water,  is  blue,  as  seen  in  the 
crevasses  and  moulins  of  glaciers,  where  the  ice  is  in 


GLACIERS   AND    ICE-SHEETS        309 

a  state  of  purity,  and  is  not  broken  up.  The  surface 
of  snow  and  ice  is  often  grey,  owing  to  accumulation 
of  dirt,  which  naturally  increases  in  amount  as 
evaporation  or  melting  progresses.  In  some  cases 
ice  has  a  green  tint,  as  described  by  Forbes  in  the 
case  of  the  crevasses  of  the  neve  of  the  Viesch 
Glacier,  and  Garwood  informs  me  that  the  crevasses 
of  some  of  the  icebergs  of  the  Spitsbergen  seas  also 
exhibit  a  green  hue,  which  must  be  due  to  some 
unexplained  condition  of  the  ice.  Lastly,  there  is 
the  red  snow,  due  to  the  occurrence  of  an  alga 
(Protococcus  nivalis}  upon  the  surface  of  the  snow. 
This  often  colours  extensive  tracts  of  snow,  and  is 
especially  noticeable  when  fresh  snow  has  fallen  over 
the  coloured  snow,  and  anyone  treads  through  the 
new  snow  and  exposes  the  coloured  snow  beneath, 
giving  rise  to  the  appearance  of  flesh-coloured  foot- 
prints upon  the  white  surface. 


CHAPTER  XVIII. 
THE  SIGNS  OF  FORMER  GLACIATION 

ONE  cannot  learn  much  of  a  watch  by  an  inspec- 
tion of  its  outer  case,  and  similarly  the  work 
of  existing  glaciers  is,  to  a  large  extent,  concealed  by 
the  mass  of  ice  beneath  which  much  of  the  work  is 
being  carried  on.  I  have,  therefore,  left  the  con- 
sideration of  the  products  of  erosion  of  ice,  and  of 
many  of  the  effects  produced  by  deposition  and  ac- 
cumlation  due  to  ice,  to  be  taken  up  when  we  proceed 
to  an  examination  of  areas  once  occupied  by  ice, 
from  which  the  ice  has  receded.  It  is  true  that 
many  of  the  effects  which  we  now  have  to  consider 
may  be  noted  at  the  termination  of  Alpine  glaciers  ; 
but  as  they  can  also  be  observed,  often  on  a  more 
imposing  scale,  in  regions  more  easily  accessible  to 
us  than  that  of  the  glaciers  of  Switzerland,  and 
especially  than  those  of  the  ice-sheets  of  Spitsbergen 
and  of  the  inland  ice  of  Greenland,  it  is  convenient 
to  call  attention  to  them  when  describing  the  results 
of  glaciation  in  regions  from  which  the  ice  has  long 
since  vanished. 

The  occurrence  of  an  Ice  Age,  or  Glacial  Period, 
in  times  which  are  geologically  recent  is  so  well 
known,  that  it  needs  no  further  reference  here  save 
to  remark  that,  owing  to  its  recency,  our  country  and 
other  glaciated  areas  had  already  acquired  physical 
310 


FORMER  GLACIATION  311 

features  differing  in  no  essential  respect  from  those 
which  they  possess  at  the  present  day ;  and  accord- 
ingly the  influence  of  ice  has  been  of  minor  import- 
ance from  a  scenic  point  of  view,  merely  modifying 
here  and  there  the  main  scenic  features  of  an  area 
which  have  been  produced  owing  to  the  operation 
of  other  agents. 

Signs  of  vanished  glaciers  in  Britain  were  first 
detected  by  Agassiz  before  the  middle  of  the  present 
century,  and  his  conclusions  were  afterwards  verified 
by  Dean  Buckland.  These  signs  may  be  considered 
under  two  heads,  namely,  features  due  to  erosion,  and 
those  due  to  accumulation. 

Glacial  Erosion. — The  signs  of  glacial  erosion  are 
very  characteristic,  and,  in  ordinary  circumstances, 
readily  recognisable.  It  is,  however,  even  now  a 
subject  of  dispute  as  to  whether  ice  is  or  is  not  a 
very  potent  factor  in  producing  erosion ;  and  although 
it  is  easy  to  point  to  evidences  of  the  erosive  action 
of  ice,  no  example  can  be  cited  which  would  be 
indisputably  regarded  as  one  of  glacial  erosion  on  a 
very  extensive  scale. 

The  main  results  of  glacial  erosion  are  the  round- 
ing, smoothing,  polishing,  and  striation  of  pre-exist- 
ing rough  surfaces.  These  results  are  due  to  the 
passage  of  ice  charged  with  rock  fragments  of  various 
sizes,  from  large  boulders  down  to  the  finest  particles 
of  dust,  over  its  rocky  bed.  Owing  to  the  great  pres- 
sure, the  rocks  of  the  bed  become  ground  down  and 
smoothed,  and  if  capable  of  receiving  a  polish,  the 
fine  particles  of  matter  carried  by  the  ice  act  like 
emery-powder,  and  produce  a  more  or  less  polished 
surface.  The  angular  grains  of  quartz  score  fine 
striations  on  the  rock-face,  and  owing  to  the  pressure 


312    SCIENTIFIC   STUDY   OF  SCENERY 

and  steady  advance  of  the  ice  these  striae  are  usually 
of  great  regularity,  many  of  them  frequently  running 
parallel  to  one  another,  and  each  being  straight,  as 
though  formed  with  a  ruler.  Larger  fragments  of 
rock  produce  larger  grooves,  sometimes  several  inches 
in  depth  and  width. 

When  a  mass  of  rock  projects  above  the  surround- 
ing ground,  the  ice  of  a  glacier  is  pressed  against 
the  side  facing  the  direction  from  which  the  ice 
comes,  and  this  side  undergoes  the  rounding  and 
smoothing  processes.  The  other  side  is  protected,  to 
some  extent,  from  the  action  of  the  ice  by  the  actual 
mass  of  rock,  and  the  ice  passes  over  it  without 
rounding  or  smoothing  it.  This  immunity  from 
erosion  may  be  increased  by  the  accumulation  of 
fragments  broken  from  the  other  side,  on  the  lee 
side,  and  these  may  act  as  a  cushion  protecting  the 
rock  beneath  from  the  action  of  the  ice.  Further- 
more, as  Mr.  P.  F.  Kendall  has  pointed  out,  the  ice 
on  the  lee  side  tends  to  tear  away  fragments  of  rock 
from  the  parent  mass,  owing  to  the  existence  of 
divisional  planes,  as  planes  of  stratification  and 
cleavage,  and  especially  of  jointing,  in  the  rock. 
Accordingly  a  projecting  rock,  after  being  acted  on 
by  a  valley  glacier,  will  be  rounded  and  smoothed  on 
the  side  facing  the  head  of  the  valley,  and  rough  and 
fractured  on  the  side  facing  the  lower  end  of  the 
valley,  as  shown  in  the  accompanying  diagram,  in 
which  the  dotted  line  indicates  the  original  irregular 
rocky  mass,  and  the  continuous  line  the  outline  which 
results  from  glacial  erosion.  (Fig.  39.)  Rocks  which 
have  been  subjected  to  glacial  erosion,  and  have  as- 
sumed this  appearance,  are  known  as  roches  inou- 
tonnees,  and  show  the  most  characteristic  effects  of 


FORMER  GLACIATION  313 

glacial  erosion.  The  upland  valleys  of  the  hilly 
districts  of  our  own  country — of  Cambria,  Cumbria, 
and  the  highlands  of  Scotland,  for  example — show 
these  roches  moutonnees  in  a  very  striking  manner, 
and  the  experienced  eye  looking  down  the  valley  will 
readily  note  the  contrast  between  the  smoothed  and 
rounded  rocks  of  the  valley  floor,  and  lower  parts  of 
of  the  valley  sides,  and  the  jagged,  frost-riven  rocks 
of  the  intervening  ridges  and  upper  portions  of  the 
valley  sides  ;  so  that  there  is  no  difficulty  in  ascer- 
taining the  height  to  which  the  ice  extended  in  the 


FIG.  39. 

case  of  a  valley  in  which  the  effects  of  glaciation 
have  not  been  removed  by  subsequent  denudation 
by  streams  and  atmospheric  agents.  It  follows  from 
what  has  been  said  concerning  the  nature  of  roches 
moutonnees,  that  this  contrast  will  not  be  marked  by 
one  looking  up  the  valley,  who  is  confronted  with  the 
rough  lee  sides  of  the  same  roches  moutonnees.  The 
nature  of  these  ice-worn  rocks  will  be  seen  in  many 
of  the  figures  illustrating  an  article  originally  written 
for  Peaks,  Passes,  and  Glaciers,  by  the  late  Sir 
Andrew  Ramsay,  and  subsequently  published  separ- 
ately under  the  title  of  The  Old  Glaciers  of  Switzer- 
land and  North  Wales,  where  also  the  other  effects  of 
glacier  action  are  admirably  described. 


3H     SCIENTIFIC   STUDY   OF   SCENERY 

The  tearing  action  noticed  on  a  small  scale  at  the 
lower  ends  of  roches  moutonnees  appears  to  be  produced 
on  a  much  larger  scale  in  the  case  of  soft  rocks,  huge 
fragments  of  these  being  torn  from  the  bed  of  the  ice 
and  transported  for  some  distance,  and  in  this  way 
irregular  hollows  of  considerable  size  may  be  formed. 

Though  the  power  of  ice  as  an  erosive  agent  has, 
as  above  remarked,  been  variously  estimated,  there 
is  no  doubt  that  the  valley  glaciers  which  once  occu- 
pied our  upland  regions  did  little  more  than  round 
off  the  minor  irregularities  of  the  original  rocky 
surface.  Pre-glacial  escarpments  may  be  often  seen, 
as,  for  instance,  in  the  beautiful  little  valley  of  Cwm 
Glas,  on  the  side  of  Snowdon,  and  on  the  plateau  in 
which  Sprinkling  Tarn  nestles  on  the  north  side  of 
Scawfell,  where  the  original  shape  of  the  cliff  formed 
by  weather  and  stream-action  is  distinctly  preserved, 
and  the  action  of  the  ice  has  been  merely  that  of 
sand-paper,  rounding  off  the  edges  of  the  pre-existing 
cliffs. 

Insignificant  as  the  action  of  ice  has  been  in  many 
places  in  directly  producing  erosion,  the  indirect 
influence  due  to  the  large  volume  of  water  which 
escapes  from  the  glaciers,  and  especially  the  angular 
nature  of  the  material  with  which  the  water  is 
charged,  must  not  be  overlooked.  Daubree  called 
attention  to  the  angular  nature  of  the  grains  of  sand 
with  which  glacier-streams  are  charged.  This  must 
materially  increase  the  corrasive  action  of  the  glacier- 
streams,  and  it  is  no  doubt  owing  to  it,  as  suggested 
in  the  eleventh  chapter,  that  those  narrow,  tortuous 
gorges  known  as  "  roflas  "  are  so  frequently  formed 
by  the  streams  of  glacier  regions. 

Another  interesting   result  of  water-erosion    in  a 


FORMER  GLACIATION  315 

district  occupied  by  glaciers  is  the  "giant's  kettle," 
which  resembles  a  pothole  produced  by  a  river,  but 
is  often  on  a  larger  scale,  and  is  frequently  found  in 
spots  where  ordinary  river  potholes  are  not  formed. 
The  giant's  kettle  is  formed  at  the  base  of  a  moulin, 
and  is  the  continuation  downward  into  the  rock  of 
the  shaft  penetrating  the  ice.  It  is  produced  by  the 
gyration  of  stones  carried  down  the  moulin  by  the 
glacier-stream,  and  owing  to  the  height  of  the  fall 
these  giants'  kettles  are  often  of  great  depth.  The 
well-known  glacier  garden  of  Lucerne  exhibits  them 
in  great  perfection,  and  instances  are  not  unknown  in 
our  own  country,  though  they  are  often  partly  de- 
stroyed by  subsequent  denudation,  and  still  more 
frequently  filled  up,  partly  by  the  stones  which  caused 
their  formation,  more  particularly,  however,  by  the 
material  which  has  been  subsequently  introduced. 

Glacial  Accumulations  and  Deposits, — The  accumu- 
lations and  deposits  which  are  due  to  ice  are  often 
of  very  considerable  importance,  on  account  of  the 
effect  which  they  produce  on  the  scenery  of  a  district. 
The  upland  valleys  of  our  own  country  are  often 
marked  by  the  moraines  which  have  been  left  behind 
on  the  retreat  of  the  ice,  in  the  way  described  in  a 
previous  chapter.  The  lateral  moraines  are  naturally 
cut  up,  to  some  extent,  by  the  streams  which  flow 
down  the  hill-sides,  but  the  terminal  moraines  are 
frequently  seen,  often  presenting  the  characteristic 
crescentic  outlines,  and  consisting  of  hummocks  com- 
posed of  incoherent  sand,  gravel,  and  boulders, 
usually  covered  with  vegetation.  Special  mention 
may  be  made  of  the  moraine  by  the  side  of  Llyn 
Llydaw,  on  Snowdon,  of  some  extensive  moraines  in 
Greenup  Gill  and  in  the  Rosthwaite  alluvial  flat  in 


316     SCIENTIFIC   STUDY   O^   SCENERY 

Borrowdale,  Cumberland,  and  more  particularly  of 
a  moraine  occurring  beneath  a  crag,  called  Wolf 
Crag,  on  the  northern  slope  of  the  Helvellyn  range, 
which  was  formed  by  a  small  corrie-glacier.  This 
moraine,  which  was  noticed  by  the  late  Mr.  Clifton 
Ward,  is  the  most  perfect  moraine  which  the  writer 
has  seen  in  this  country,  and  it  is  \vell  worth  a 
visit  by  those  who  are  interested  in  glacial  action. 
Along  the  summit  of  it  runs  the  old  hill-road  from 
Patterdale  to  Keswick,  and  it  may  easily  be  reached 
from  the  latter  place. 

It  has  been  noted  in  another  chapter  that  moraine- 
like  accumulations  may  be  formed  at  the  foot  of  a 
corrie  by  the  sliding  of  material  down  snow-slopes, 
and  that  moraines  may  be,  to  some  extent,  simulated 
in  other  ways. 

Another  very  interesting  effect  of  glaciation  is  the 
deposit  of  isolated  blocks  of  rock,  often  of  large  size, 
on  the  summits  and  sides  of  prominent  elevations. 
As  the  ice  gradually  recedes  these  blocks  are  left 
stranded  in  places  where  they  could  not  have  rested 
unless  gently  deposited.  They  are  known  as  perched 
blocks,  and  produce  a  very  marked  effect  upon  the 
scenery  of  some  valleys.  They  are  especially  notice- 
able in  the  Pass  of  Llanberis,  and  it  is  somewhat 
remarkable,  as  pointed  out  by  Ward,  that  they  are 
comparatively  rare  in  the  Lake  District.  Many  of 
them  occur,  however,  around  Scawfell,  especially  on 
the  plateau  below  Great  End. 

Away  from  the  regions  formerly  occupied  by  valley 
glaciers  we  find  extensive  accumulations  of  glacial 
origin,  known  as  boulder-clay  or  till.  This  boulder- 
clay  usually  consists  of  a  clayey  or  sometimes  of  a 
sandy  matrix  charged  with  angular  and  subangular 


FORMER   GLACIATION  317 

fragments  (the  latter  often  striated)  of  various  sizes, 
and  the  accumulation  usually  shows  no  signs  of 
stratification.  Some  of  it  is  undoubtedly  the  result 
of  the  melting  of  inland  ice,  and  the  deposit  of  the 
material  carried  beneath,  within,  and  in  some  cases 
above  the  ice,  upon  the  ground  formerly  occupied  by 
that  ice.  In  other  cases  it  may  be  a  glacio-marine 
deposit.  Occasionally  it  has  been  laid  down  as 
ridges,  locally  known  as  drumlins,  but  it  often  forms 
an  extensive  deposit,  the  upper  part  of  which  is 
roughly  parallel  to  the  original  surface  of  the  ground, 
though  minor  inequalities  are  often  concealed  owing 
to  excessive  accumulation  of  material  within  them, 
and  on  account  of  this,  as  previously  shown,  exten- 
sive changes  in  the  direction  of  our  river-drainages 
have  been  brought  about,  and  lakes  have  also  been 
produced  in  many  cases. 

On  account  of  the  character  of  the  boulder-clay,  it 
frequently  illustrates  the  nature  of  water-erosion,  oc- 
curring subsequently  to  its  formation,  in  a  very 
marked  manner.  This  is  beautifully  shown  along 
the  Yorkshire  coast,  especially  when  boulder-clay 
rests  upon  the  chalk.  The  chalk  has  been  worn 
away  along  dominant  planes  of  stratification  and 
jointing,  but  the  more  homogeneous  boulder-clay 
above  has  been  carved  into  little  hills  and  ridges, 
showing  the  characteristic  curves  of  water-erosion, 
and  the  ridges  are  so  sharp  that  they  imitate  on  a 
small  scale  the  aretes  of  an  alpine  region. 

The  existence  of  ridges  of  incoherent  material 
which,  has  been  accumulated  upon  the  original 
surface,  is  very  frequent  in  a  region  which  has  been 
subjected  to  former  glaciation.  Two  kinds  of  ridges 
have  already  been  noted,  namely,  the  moraine  and 


3i8     SCIENTIFIC   STUDY   OF   SCENERY 

the  drumlin.  Other  ridges  consist  of  stratified 
deposits  of  sand  and  gravel,  and  are  spoken  of 
variously  as  kames,  eskers,  and  asar,  and  to  these 
we  must  now  direct  our  attention.  The  terms  kame 
and  esker  have  been  applied  somewhat  loosely  to 
various  kinds  of  ridges  of  stratified  material,  some  of 
which  are  almost  certainly  of  fluviatile  origin,  formed 
as  ridges  between  two  adjacent  rivers,  often,  no  doubt, 
emanating  from  a  retreating  ice-mass.  Others,  how- 
ever, cannot  be  explained  in  this  way,  and  though 
an  attempt  has  been  made  to  show  that  they  are 
of  marine  origin,  all  the  evidence  is  against  this 
mode  of  their  formation.  Eskers  of  this  nature  are 
specially  well  -  developed  in  the  central  plain  of 
Ireland,  and  they  resemble  in  all  respects  except 
size  the  asar  of  Scandinavia.  They  frequently 
ramify,  and  the  tributary  eskers  join  the  main  ones 
as  the  tributaries  of  a  river  join  the  main  stream. 
Again,  they  often  show  the  tortuous  course  of  a 
river,  sometimes  possessing  actual  loops.  The  steep 
inclination  of  their  sides,  the  general  slope  of  the 
strata  at  the  sides  in  a  direction  parallel  to  the 
surface  of  the  ridge,  and  the  frequent  existence  of 
erratic  blocks  of  glacial  character  on  their  summits 
and  sides,  forbids  the  supposition  that  they  were 
produced  by  ordinary  rivers,  and  suggests  formation 
by  rivers  which  were  confined  at  the  sides  by  steep 
walls  which  have  since  disappeared.  Again,  they 
frequently  run  across  irregularities  of  the  ground, 
sometimes  actually  traversing  the  present  valleys 
at  right  angles  to  their  general  directions,  and 
passing  over  the  intervening  ridges  which  separate 
the  valleys.  For  these  and  other  reasons  Hummel 
maintained  that  they  were  the  result  of  accumulation 


FORMER   GLACIATION  319 

in  englacial  streams,  and  Professor  Sollas  has  sub- 
sequently applied  this  view  to  account  for  the 
principal  eskers  of  the  central  plain  of  Ireland,1 
and  it  is  certainly  supported  by  the  recent  exam- 
ination of  the  Malaspina  glacier,  which  induced 
Russell  to  adopt  the  same  explanation,  which, 
indeed,  accounts  for  all  the  peculiarities  of  esker- 
formation  and  distribution. 

The  filling  of  hollows  by  boulder-clay  is  a  potent 
factor  in  giving  rise  to  a  plain  surface,  as  the  result 
of  the  spread  of  boulder-clay  over  a  pre-existing 
irregular  surface  ;  and  the  deposit  of  fluvio-glacial 
materials  forms  a  still  more  pronounced  plain. 
Reference  has  already  been  made  to  plains  formed 
in  this  manner  in  extra-British  territories,  but  it  is 
a  moot  point  how  far  some  of  our  flats  have  been 
produced  by  levelling  of  irregular  surfaces  by 
fluvio-glacial  deposit  as  opposed  to  true  glacial 
deposits,  whether  terrestrial  or  marine.  There  is  no 
doubt  that  some  of  the  minor  flats  of  an  upland  region 
owe  their  character  to  the  accumulation  of  fluvio- 
glacial  deposit,  but  the  late  Professor  Carvill  Lewis 
maintained  that  much  of  the  boulder-clay  of  the 
Eastern  and  Midland  Counties  of  England  was  also 
of  fluvio-glacial  origin,  a  view  which,  though  not 
generally  accepted,  has  by  no  means  been  disproved. 

One  other  possible  result  of  glaciation  may  be 
noted.  It  is  well  known  that  many  plants  which 
are  found  in  alpine  regions  are  still  found  lingering 
in  the  upland  regions  of  Britain.  Among  them  may 
be  mentioned  Saxifraga  oppositifolia,  Gentiana  verna, 
G.  nivalis,  Silene  acaulis,  and  Lloydia  serotina.  Any- 
one who  has  seen  the  first-mentioned  plant  on  the 

1  SOLI.AS,  W.  J.,  /•«'.  Trans.  Roy.  Dublin  Soc.,  ser.  2,  vol.  v.,  p.  786. 


320     SCIENTIFIC   STUDY   OF   SCENERY 

rocks  of  some  of  the  recesses  of  Snowdonia,  occurring 
in  great  patches,  with  its  reddish-purple  flowers  spread 
over  a  considerable  space  in  the  early  spring,  or  who 
has  seen  the  blossoms  of  the  spring  gentian,  with 
their  exquisite  blue  colour,  lighting  up  the  slopes 
of  Teesdale,  will  admit  that  these  flowers  produce  a 
distinct  effect  upon  the  scene.  It  has  been  maintained 
that  these  plants  were  distributed  through  the  interven- 
ing lowlands  during  the  cold  of  the  Ice  Age,  and  that 
on  the  amelioration  of  the  climate  they  disappeared 
from  the  lowlands,  but  lingered  on  in  the  uplands. 
This  explanation  has,  perhaps,  not  been  completely 
proved  to  be  the  true  one,  but  it  may  be  mentioned 
as  a  possible  cause  of  the  existence  in  Britain  of  a 
group  of  plants  which  exercises  a  strange  fascination 
on  the  mind  of  the  botanist  and  of  the  lover  of 
mountain  scenery. 


CHAPTER   XIX. 
THE   OCEANS 

A 'ART  from  the  play  of  colour  upon  the  surface 
of  the  ocean,  and  the  variety  presented  by  the 
appearance  of  that  surface,  at  one  time  glassy  calm, 
at  another  ruffled  by  the  wind,  or  churned  into  foam 
or  spin-drift  by  the  tempest,  the  effect  of  the  present 
oceans  in  influencing  scenery  is  confined  to  the  coast- 
lines which  form  the  ocean  margins,  and  to  these  we 
shall  have  to  direct  our  attention  more  particularly. 

Still  water  has  comparatively  little  effect  in  chang- 
ing the  character  of  the  surrounding  land.  A  little 
chemical  solution  of  rocks  no  doubt  takes  place,  but 
it  is  a  change  which  may  be  neglected  for  our  present 
purposes,  and  we  must  devote  attention  to  the 
changes  which  result  from  the  ocean  movements. 
These  movements  are  of  three  kinds,  namely,  waves, 
tides,  and  currents,  and  each  plays  its  part  in  modify- 
ing the  scenery  of  the  earth's  surface,  waves  being 
specially  effective  as  agents  of  erosion,  while  tides  and 
currents  play  the  chief  part  in  transporting  material 
which  has  already  been  eroded. 

It  is  of  importance  to  our  inquiry  that  we  should 
obtain  some  notion  of  the  true  nature  of  a  wave,  and 
a  few  words  must,  therefore,  be  here  devoted  to  this 
topic.  A  wave  has  been  defined  as  "a  system  of 
movements  in  which  the  several  particles  move  to 
Y  321 


322     SCIENTIFIC   STUDY   OF   SCENERY 

and  fro,  or  round  and  round,  about  definite  points,  in 
such  a  manner  as  to  produce  the  continued  onward 
transmission  of  a  condition  or  series  of  conditions." 
The  reader  will  notice  that  the  condition  or  con- 
ditions are  transmitted  and  not  the  particles.  This 
is  well  illustrated  when  the  wind  is  blowing  over  a 
hayfield  or  cornfield.  The  onward  movement  of  the 
waves  is  clearly  seen,  but  it  is  equally  clear  that  the 
particles  composing  the  blades  of  grass  or  corn  do 
not  move  on  with  the  waves,  each  one  returning  to 
its  place  after  a  wave  has  passed.  Again,  a  cork 
floating  on  the  sea  bobs  up  and  down  as  the  wave 
passes,  but  there  is  no  onward  movement  of  the 
cork,  if  it  be  floating  where  the  water  is  deep  some 
distance  from  the  land.  As  a  matter  of  fact  the  cork 
does  not  merely  bob  up  and  down,  it  describes  a 
circle,  and  a  similar  circle  is  described  by  a  particle 
of  water  on  the  surface  during  the  passage  of  a  wave. 
A  complete  wave  consists  of  a  trough  in  front  and 
an  arch  behind,  and  a  wave-length  is  the  distance 
from  the  crest  of  one  arch  to  the  crest  of  a  succeeding 
one,  or  from  any  point  on  one  wave  to  that  point 
on  the  adjoining  one  which  is  moving  in  the  same 
manner,  while  the  amplitude  of  the  wave  is  the 
vertical  distance  from  the  level  of  the  wave  crest  to 
that  of  the  wave  trough.  Supposing  a  particle  to  be 
situated  in  the  centre  of  the  front  slope  of  an 
advancing  arch  of  the  wave.  This  particle  moves 
forward  through  a  quadrant  of  a  circle  till  it  is 
situated  on  the  summit  of  the  crest,  it  then  moves 
backward  through  another  quadrant,  until  situated 
in  the  centre  of  the  hinder  slope  of  the  advancing 
arch,  still  backward  through  another  quadrant,  until 
at  the  bottom  of  the  trough  of  the  succeeding  wave, 


THE   OCEANS  323 

and  then  forward  through  a  fourth  quadrant,  which 
places  it  in  the  centre  of  the  forward  slope  of  the 
advancing  arch  of  this  wave ;  it  has  now  moved 
through  a  circle  and  reached  its  initial  position. 

Ordinary  sea-waves  are  produced  by  wind  blowing 
on  the  surface,  and  owing  to  the  friction  the  water 
is  thrown  into  a  series  of  undulations,  which  may 
travel  onwards  beyond  the  area  in  which  they  were 
produced,  with  ever  diminishing  intensity ;  they  are 
then  known  as  ground-swell.  Tidal  waves,  due  to 
the  action  of  the  sun  and  moon,  differ  from  wind- 
waves  in  their  length,  which  is  enormous  as  compared 
with  their  amplitude,  and  accordingly  particles  are 
moved  in  flattened  ellipses,  and  considerable  forward 
and  backward  movements  of  bodies  of  water  occur 
as  tidal  currents.  When  a  tidal  wave  enters  a 
narrow  estuary  the  arch  of  the  wave  is  forced  forward 
upon  the  trough,  giving  rise  to  a  bore  or  aegre,  which 
breaks  upon  the  shore  of  the  estuary,  and  accord- 
ingly exercises  effects  comparable  with  those  of 
wind-waves,  which  will  be  presently  discussed.  These 
bores  are  well  known  in  many  parts  of  the  world,  the 
best  known  being  those  of  the  Bay  of  Fundy  in 
Nova  Scotia,  the  Hooghly  in  north-western  India,  and 
the  Severn  in  our  own  country.  When  the  tidal  wave, 
thus  influenced  by  the  shape  of  the  coast,  attains 
different  heights  in  two  adjacent  tracts  of  water 
united  by  narrow  straits,  the  difference  of  level  is 
atoned  for  by  a  current  flowing  through  the  straits 
from  the  higher  to  the  lower  tract  of  water  as  a 
race.  As  the  tract  which  has  the  highest  tide  has 
also  the  lowest,  the  direction  of  the  race  is  reversed 
with  change  of  tide.  The  eddies  produced  along  the 
coasts  in  a  race  give  rise  to  whirlpools  like  the  well- 


324     SCIENTIFIC   STUDY   OF   SCENERY 

known  Maelstrom,  and  when  the  race  is  moving 
against  a  wind  the  resultant  waves  are  of  exceptional 
size  and  violence. 

Ocean  currents  are  produced  in  various  ways. 
Some,  as  already  stated,  are  due  to  differences  in  the 
height  of  the  tide  in  adjoining  areas.  Others  are 
marked  by  differences  of  saltness  of  adjoining  tracts 
of  water  depending  upon  greater  evaporation  in  one 
place  than  another,  as  in  the  case  of  the  surface 
current  flowing  to  the  more  saline  waters  of  the 
Mediterranean  from  the  less  salt  Atlantic  Ocean, 
through  the  Straits  of  Gibraltar,  or  upon  slight  evapo- 
ration which  cannot  remove  the  excessive  amount  of 
fresh  water  poured  in  by  rivers,  as  in  the  case  of 
the  surface  current  which  flows  out  of  the  fresher 
Baltic  to  the  more  saline  North  Sea.  The  principal 
oceanic  currents  which  flow  upon  the  surface  are,  as 
is  now  generally  agreed,  due  to  surface  winds.  A 
temporary  wind  produces  a  temporary  current,  a 
periodical  wind  a  periodical  current,  and  a  permanent 
wind  a  permanent  current.  All  of  these  currents 
are  important  as  transporting  agents,  which  carry 
denuded  material  from  one  place  to  another. 

Having  briefly  considered  the  nature  of  the  prin- 
cipal agents  of  marine  denudation,  we  may  now  turn 
to  an  examination  of  their  effects.  The  principal 
work  is  the  destruction  of  coast-lines  and  the  re- 
moval of  this  material  (as  well  as  of  that  which  is 
produced  by  the  agents  of  subaerial  denudation)  to 
other  places,  where  it  is  deposited. 

The  most  effective  agents  in  denuding  the  coast- 
line are  the  waves  of  the  sea.  It  has  been  seen  that 
in  the  open  ocean  the  effect  of  a  wave  is  to  give  a 
particle  a  circular  motion  and  to  restore  it  to  its 


THE   OCEANS  325 

original  position  when  the  wave  has  passed.  As  the 
wave  reaches  shallow  water  the  lower  part  of  the  wave 
is  retarded  by  friction  against  the  bottom  and  the 
upper  part  moves  over  it,  so  that  we  find  actual 
onward  translation  of  particles  of  a  wave,  whether  an 
ordinary  wind- wave  or  one  which  belongs  to  the 
ground-swell,  and  the  upper  part  is  often  carried 
forward  until  it  breaks  at  the  crest,  causing  a 
"  breaker."  Any  solid  matter  suspended  in  the  water, 
as  a  grain  of  sand  or  a  pebble,  likewise  acquires  this 
motion  of  translation,  becoming  hurled  forward,  and 
it  is  on  account  of  these  fragments  of  rock  being 
hurled  against  the  coast-lines  that  much  of  the 
waste  of  the  coast  is  produced. 

One  often  hears  persons  speaking  glibly  of  waves 
running  "  mountains  high,"  but,  as  a  matter  of  fact, 
the  greatest  height  attained  by  wind-waves  does  not 
appear  to  exceed  fifty  feet  in  the  open  ocean,  though 
when  the  waves  break  masses  of  foam  and  splashes 
of  water  are  frequently  carried  to  heights  of  over 
100  feet  "  During  north-westerly  gales  the  windows 
of  the  Dunnet  Head  lighthouse,  at  a  height  of 
upwards  of  300  feet  above  high-water  mark,  are  said 
to  be  sometimes  broken  by  stones  swept  up 
the  cliffs  by  the  sheets  of  sea-water  which  then 
deluge  the  building."1 

It  is  also  important  for  us  to  have  some  idea  of  the 
depth  below  the  general  surface  of  the  water  to 
which  the  influence  of  these  sea- waves  extends.  The 
reason  why  this  is  important  will  appear  in  the 
sequel,  in  the  meantime  it  may  be  stated  that  the 
wind-wave  is  a  superficial  phenomenon.  Although 
there  is  evidence  of  gentle  movement  being,  produced 

1  GEIKIE,  Sir  A.,  Text  Book  of  Geology,  3rd  edition,  p.  437. 


326     SCIENTIFIC   STUDY   OF   SCENERY 

by  waves  to  a  depth  of  over  600  feet,  the  distance 
below  the  surface  at  which  waves  can  produce 
appreciably  erosive  effect  on  hard  rock  is  probably 
very  much  less  than  this,  and  various  statements 
made  by  engineers  seem  to  indicate  that  at  a  depth 
of  considerably  less  than  100  feet  the  erosive  effect 
of  waves  is  practically  unimportant. 

The  force  of  the  waves  has  also  been  calculated 
in  many  cases.  "  A  single  roller  of  the  ground-swell, 
twenty  feet  high,  falls,  according  to  Mr.  Scott 
Russell,  with  a  pressure  of  about  a  ton  on  every 
square  foot.  Mr.  Thomas  Stevenson  conducted 
some  years  ago  a  series  of  experiments  on  the 
force  of  the  breakers  on  the  Atlantic  and  North 
Sea  coasts  of  Britain.  The  average  force  in  summer 
was  found  in  the  Atlantic  to  be  611  Ibs.  per  square 
foot,  while  in  the  winter  it  was  2086  Ibs.,  or  more 
than  three  times  as  great.  On  several  occasions, 
both  in  the  Atlantic  and  North  Sea,  the  winter 
breakers  were  found  to  exert  a  pressure  of  three 
tons  per  square  foot,  and  at  Dunbar  as  much  as 
three  tons  and  a  half."1 

In  considering  the  effect  of  waves,  the  influence 
of  the  comparatively  rare,  but  exceptionally  large, 
earthquake  waves  which  sometimes  break  upon 
coasts  must  not  be  forgotten.  They  no  doubt 
largely  assist  the  work  of  erosion  in  regions  subject 
to  earthquakes. 

That  waves  hurled  against  the  coast-line  with  the 
force  which  has  been  indicated  above  must  produce 
great  destruction  is  obvious.  Nevertheless,  the 
destruction  is  largely  due,  not  to  the  water  itself, 
but  to  the  solid  matter  which  is  held  up  by  the 
1  GEIKIE,  Sir  A.,  loc.  cit. 


THE   OCEANS  327 

water.  This  solid  matter,  which  normally  forms  a 
beach,  is  not  always  present ;  the  mode  of  its 
arrangement  as  beach-material  will ,  be  considered 
eventually.  Where  it  is  absent,  as,  for  instance, 
where  the  sea  coast  plunges  suddenly  down  into 
deep  water,  comparatively  little  erosion  by  wave 
action  may  be  produced. 

An  ideal  uplift,  as  has  been  observed,  would 
consist  of  a  tract  of  land  having  a  convex  surface 
sloping  from  the  centre  seaward,  and  the  curve 
would  be  continued  below  sea-level ;  there  would  be 


b 

FIG.  40. 


no  sea-cliff.  In  Fig.  4O,1  let  the  line  ab  represent 
part  of  such  a  land,  s  s  being  sea-level,  and  X  X  the 
height  above  which  the  waves  could  not  act.  The 
waves,  charged  with  sand  and  pebbles,  would 
gradually  wear  away  the  land  as  shown  by  the 
dotted  lines,  causing  the  upper  part  to  overhang. 
(They  would  also  wear  away  material  below  sea- 
level  to  the  depth  at  which  their  erosive  action 
became  ineffective,  but  this  action  we  may  for  the 
present  ignore.)  The  overhanging  portion  could  not 
be  prolonged  indefinitely,  and  eventually  the  upper 
part  would  fall  away,  giving  rise  to  landslips.  In 
nature  it  is  usually  removed  more  gradually,  for 
reasons  which  will  presently  be  stated.  When  the 
overhanging  part  opq  had  fallen  and  been  washed 

1  The  lines  X  X  and  s  s  should  be  horizontal  in  the  figure. 


328     SCIENTIFIC   STUDY   OF   SCENERY 

away,  a  sea-cliff,  op  r,  would  be  produced,  and  the 
process  would  go  on  as  before.  If,  therefore,  the 
action  of  the  sea-waves  alone  produced  cliffs,  we 
should  expect  to  find  a  coast-line  marked  by  cliffs, 
which  overhang  above  the  base  in  places,  while  in 
other  places,  where  the  material  had  fallen  and  been 
removed,  there  would  be  no  overhanging.  Now  an 
overhanging  cliff  is  comparatively  rare,  and  it  is 
obvious  that  some  other  operation  or  operations 
besides  the  action  of  the  waves  are  concerned  with 
the  erosion  of  coast  lines. 

A  good  illustration  of  an  overhanging  cliff,  under- 
cut at  the  base  by  the  waves,  has  recently  been 
furnished  by  Mr.  C.  W.  Andrews  in  Christmas 
Island,  an  island  in  the  Indian  Ocean.  "  The  shore 
terrace  slopes  gently  down  from  the  foot  of  the  first 
inland  cliff  to  the  sea-cliff,  which  is  from  fifty  to 
eighty  or  more  feet  high,  and  is  often  undercut  by 
the  waves  to  a  remarkable  extent,  so  that  it  some- 
times overhangs  more  than  twenty  feet."1 

On  examining  sea-cliffs  we  soon  find  that  the  out- 
line of  the  cliff  is  largely  determined  by  the  nature  and 
trend  of  the  divisional  planes  by  which  the  rocks  are 
affected,  especially  the  planes  of  stratification,  and 
more  particularly  the  joints.  When  the  joints  are 
inclined  seawards  a  cliff  is  formed  sloping  towards 
the  sea  (Fig.  41  a),  if  the  joints  are  vertical,  though 
the  cliff  will  probably  not  be  vertical  it  will  tend  to 
consist  of  a  series  of  steps,  portions  of  which  ap- 
proach verticality  (Fig.  41  b],  while  if  the  joints  are 
inclined  towards  the  land  portions  of  the  cliff  may 
actually  overhang.  (Fig.  41  c.} 

1  ANDREWS,  C.  W.,  Geographical  Journal,  vol.  xiii.,  No.  I  (Jan., 
1899),  p.  24  ;  see  also  illustrations  on  pp.  23  and  27. 


THE   OCEANS 


329 


The  dependence  of  cliff  outline  upon  joints  is  thus 
well  exhibited.1 

As  the  upper  parts  of  these  cliffs  are  frequently 
above  ordinary  wave  action,  it  is  clear  that  their 
outlines  at  the  upper  parts  are  not  directly  deter- 
mined by  this  action,  and  inspection  of  the  cliffs 
will  show  that  in  many  cases  subaerial  agents  are 
responsible  for  their  backward  wear.  But  in  addition 
to  this  there  is  another  process  which  comes  into 
play  in  the  formation  of  sea-cliffs,  to  which  we 
must  briefly  refer.  The  waves  themselves  wear 
away  material  more  easily  when  affected  by  divisonal 


planes  than  when  it  is  not  so  affected.  Suppose  the 
cliff  in  Fig.  42  has  a  plane  of  stratification  or  an 
easily  denuded  stratum  s,  below  high  tide  level  h  h, 
and  above  the  level  of  low  tide.  The  rock  will  be 
more  easily  denuded  along  this  plane  of  weakness, 
and  a  cavern  may  be  worn  out,  as  shown  by  the 
shaded  portion  c.  Such  caves  will  be  specially  prone 
to  occur  where  downward  joints,  traversing  the  cliffs 
vertically,  coincide  with  a  stratification  plane  at  the 
base,  and  they  are  very  numerous  around  sea-coasts. 
If  another  joint  /  be  encountered  after  the  cave  has 
been  worn  some  distance  inward,  the  erosive  action 

1  On  this  subject  the  reader  may  well  consult  an  article  by  Sir  A. 
Geikie  on  "  The  Old  Man  of  Hoy,"  in  his  Geological  Sketches  at  Home 
and  Abroad,  p.  26. 


330    SCIENTIFIC   STUDY   OF   SCENERY 

will  be  facilitated  by  it,  and  an  upward  extension  of 
the  cavern  will  be  here  formed,  as  shown  by  the 
shaded  portion  c.  This  may  grow  upward  until  it 
reaches  the  surface,  when  during  high  tide  the  water 
will  be  forced  up,  and  issue  on  the  surface  of  the 
cliff  some  distance  away  from  the  edge  as  a  jet  of 
water.  This  is  a  blow-hole  or  puffing-hole,  and 
these  blow-holes  are  often  found  behind  high  cliffs, 
even  some  way  from  the  edge.  Many  of  them  occur 


J 


FIG.  42. 

round  the  Irish  coast,  as  indicated  in  the  following 
description  given  by  the  late  Professor  J.  B.  Jukes  in 
his  Manual  of  Geology  : — 

"  At  the  promontory  of  Loop  Head,  Mr.  Marcus  Keane 
has  observed  that  considerable  blocks  of  rock  have  been 
blown  into  the  air  on  the  formation  of  one  of  these 
puffing-holes,  and  that  large  holes,  opening  down  into 
cavernous  gullies,  lead  from  one  cove  to  another,  behind 
bold  headlands  of  over  a  hundred  feet  in  height,  showing 
how  the  land  is  undermined  by  the  sea,  and  headlands 
gradually  made  into  islands.  One  such  square  precipitous 


THE   OCEANS  331 

island,  which  is  now  at  least  twenty  yards  from  the  main- 
land, was  said  by  the  farmer  who  held  the  ground  to  have 
been  accessible  by  a  twelve-foot  plank  when  he  was  a  boy. 
Mr.  W.  L.  Wilson,  late  of  the  Geological  Survey  of  Ire- 
land, found  in  the  far  part  of  the  promontory  between 
Bantry  and  Dunmanus  Bays,  dark  holes  in  the  fields  some 
distance  back  from  the  edge  of  the  cliffs,  looking  down 
into  which  the  sea  might  be  dimly  seen  washing  back- 
wards and  forwards  in  the  narrow  caverns  below.  In 
County  Kerry,  Ballybunnion  Head  is  completely  under- 
mined by  caverns,  into  which  the  sea  enters  from  both 
sides.  The  whole  coast  of  Clare,  and  of  the  Arran  Islands, 
is  a  succession  of  precipitous  cliffs  with  vertical  faces,  the 
result  of  the  sea  acting  on  the  large  cuboidal  joints  that 
traverse  the  rocks.  The  celebrated  rocks  of  Moher  in  that 
county,  which  rise  with  a  perfectly  vertical  face  to  heights 
of  more  than  600  feet,  afford  magnificent  examples  of  the 
way  in  which  the  ocean  takes  advantage  of  the  joint 
structure  to  cut  back  into  the  land,  however  lofty  or  how- 
ever hard  and  unyielding  it  may  apparently  be." 

Much  of  the  erosive  action  above  described  is  due 
to  the  compression  of  air,  when  the  waves  enter  the 
cave  at  high  water.  In  Fig.  42  the  cave  c  being  full 
of  water,  when  a  wave  comes  in,  the  water  in  the 
part  c  rises  and  compresses  the  air  above,  and  this 
sudden  compression  may  force  off  a  great  mass  of 
rock  between  the  joint  j  and  the  face  of  the  cliff. 

The  dominant  joints  which  run  down  the  face  of 
a  cliff  facilitate  erosion,  and  determine  the  formation 
of  the  narrow  chimneys  which  often  seam  the  faces 
of  a  cliff. 

When  a  mass  of  rock  juts  out  as  a  promontory, 
a  cavern  may  be  drilled  through  this  promontory, 
and  on  enlargement  an  arch  will  be  formed.  Such 


332     SCIENTIFIC   STUDY   OF  SCENERY 

arches  are  frequently  found  on  our  coast-lines,  as  for 
instance,  on  the  Durham  coast,  that  of  the  Isle  of 
Wight,  and  that  of  Pembrokeshire.  If  the  top  of 
the  arch  falls  in,  an  isolated  "  stack  "  or  "  needle  "  is 
formed,  or  the  same  may  be  due  to  the  cutting 
through  of  a  promontory  along  a  vertical  plane  of 
weakness,  without  the  preliminary  formation  of 'the 
arch.  Examples  of  this  are  furnished  by  the  Needles 
of  the  Isle  of  Wight,  and  the  more  remarkable 
Eligug  Stacks  carved  out  of  the  mountain  limestone 
of  the  Pembrokeshire  coast. 

When  the  land  is  composed  of  soft  rocks,  sub- 
aerial  erosion  may  produce  a  gentle  slope  above,  just 
as  it  does  inland,  and  then  the  sea -cliff  is  absent. 
This  is  seen  in  many  parts  of  the  east  coast  of 
England,  which  is  largely  composed  of  soft  rocks, 
but  even  these,  when  devoid  of  divisional  planes  and 
composed  of  stiff  clay,  may  give  rise  to  cliffs,  as  in 
many  places  where  the  coast  consists  of  boulder- 
clay. 

When  the  strata  dip  gently  towards  the  sea,  and 
porous  strata  rest  on  impervious,  the  conditions  are 
favourable  for  landslips,  just  as  they  are  inland,  and 
accordingly  landslips  may  and  do  occur  in  these 
circumstances,  like  that  which  recently  took  place 
at  Sandgate,  or  the  more  classic  one  of  Axmouth, 
in  Dorsetshire,  which  produced  a  very  marked  effect 
upon  the  scenery,  owing  to  the  way  in  which  the 
fallen  mass  became  fissured  and  displaced. 

It  has  been  observed  that  the  denuded  material 
may  or  may  not  accumulate  at  the  margin  of  the 
land  to  form  beaches.  If  beaches  are  formed,  their 
existence  for  some  time  facilitates  erosion,  as  they 
furnish  material  which  may  be  hurled  by  the  waves 


THE   OCEANS  333 

against  the  land  behind,  but  if  the  amount  of  material 
which  accumulates  is  excessive,  it  acts  as  a  break- 
water, and  retards  erosion,  instead  of  facilitating  it. 

We  have  now  considered  the  formation  of  the 
sea-cliff  with  its  attendant  phenomena  of  chimneys, 
caverns,  blow-holes,  arches,  stacks  and  needles, 
and  are  in  a  position  to  proceed  to  a  considera- 
tion of  the  character  of  coast-lines  as  a  whole 
and  the  way  in  which  they  are  partly  dependent 
upon  the  transport  of  material  by  the  action  of 
currents.  In  order  to  do  this  we  must  pay  some 
attention  to  the  mode  of  formation  of  beaches,  which 
has  only  been  alluded  to  in  very  general  terms. 
Two  important  memoirs  upon  beaches  have  ap- 
peared, in  which  the  student  will  find  much  informa- 
tion concerning  their  detailed  structure,  one  by 
Dr.  G.  K.  Gilbert,  "  On  the  Topographical  Features 
of  Lake  Shores,"1  and  the  other  by  Mr.  Vaughan 
Cornish,  "  On  Sea  Beaches  and  Sandbanks."2 

The  first  point  to  notice  in  the  formation  of  a 
beach  is  the  sorting  of  the  material.  It  is  generally 
known  that  the  coarse  material  is  mainly  deposited 
near  the  shore,  and  the  finer  out  to  sea,  and  the 
explanation  which  is  usually  given  to  account  for 
this  is  that  the  fragments  are  dropped  according 
to  their  size  and  weight.  Though  this  is  true,  it  is 
by  no  means  the  whole  truth,  and  many  other  causes 
contribute  to  the  sorting,  to  some  of  which  reference 
must  be  made,  though  the  student  should  consult 
Mr.  Cornish's  paper  for  full  details.  When  a  wave 

1  GILBERT,  G.  K.,  Fifth  Annual  Report  of  the  U.S.  Geological 
Survey. 

3  CORNISH,  V.,  Geographical  Journal,  vol.  xi.  (1898),  No.  5, 
p.  528,  and  No  6,  p.  628. 


334    SCIENTIFIC   STUDY   OF   SCENERY 

breaks  upon  the  shore,  the  forward  velocity  of  the 
crest  of  the  wave  is  greater  than  the  backward 
velocity  of  the  under  part.  The  latter  is  often 
spoken  of  as  undertow,  though  there  are  really  two 
distinct  movements.  Now  if  the  velocity  of  the  on- 
shore movement  be  sufficient  to  calrry  forward  sand 
and  pebbles,  and  that  of  the  off-shore  movement  be 
sufficient  to  carry  sand  and  not  pebbles,  the  pebbles 
will  be  deposited  on  the  beach,  and  the  sand  carried 
back.  Again,  when  a  pebble-beach  is  formed,  much 
of  the  water  percolates  through  the  pebbles  on  its 
way  back,  and  is  unable  to  carry  pebbles  with  it. 
The  sand,  kept  in  suspension  for  a  considerable  period 
by  eddies,  is  often  carried  some  way  out,  and  owing 
to  its  inertia  is  borne  for  some  distance  onward, 
when  the  current  is  checked  or  turned,  and  settles 
in  sandbanks.  All  the  fragments,  whether  of  pebble, 
sand,  or  mud,  are  moved  while  raised  from  the 
bottom  by  the  eddies  which  are  set  up  during  the 
passage  of  waves.  With  the  heavier  pebbles,  the 
period  of  lifting  is  short,  with  sand  longer,  but  with 
mud  so  long  that,  according  to  Mr.  Cornish,  the  mud 
forms  an  emulsion  in  the  water,  and  "  the  transit  of 
mud  down  the  slope  from  the  shore  is  not  due  to  the 
action  of  gravity,"  but  "  the  principal  factor  in  de- 
termining the  well-known  direction  of  mud-transport 
is  the  diminution  of  intensity  of  bottom  agitation 
from  the  shallows  to  the  depths." 

The  cross  section  of  a  beach  is  often  very  com- 
plicated, small  beaches  being  frequently  superposed 
upon  the  larger  ones,  but  the  general  profile  of  a 
beach  as  seen  in  cross-section  is  a  flattened  sigmoidal 
curve. 

More  important  from  the  scenic  point  of  view  than 


THE   OCEANS  335 

the  varieties  of  structure  of  a  beach  (which  are  fully 
considered  in  Mr.  Cornish's  paper)  is  the  wandering 
of  beach-materials  along  shore,  which  is  determined 
by  currents,  whether  tidal  or  due  to  the  prevailing 
winds.  A  wind  blowing  towards  the  shore,  and  not 
at  right  angles  to  the  direction  of  the  coast,  sets  up 
a  current  which,  when  it  reaches  the  coast,  moves 
along  it,  parallel  to  its  direction  and  in  the  general 
direction  of  the  wind  which  caused  it.  Owing  to 
this  current  the  beach-material  is  gradually  carried 
along  the  shore,  and  if  the  coast-outline  is  com- 
paratively regular,  the  pebbles  are  swept  along  the 
pre-existing  coast-line.  When  there  is  a  deep  in- 
dentation, however,  the  material  is  carried  onward, 
owing  to  inertia,  and  builds  up  a  shingle  spit,  which 
may  be  eventually  carried  right  across  a  bay  and 
convert  it  into  a  lagoon,  or  may  be  carried  from 
mainland  to  island,  or  vice  versa,  or  both,  eventually 
converting  the  island  into  a  peninsula,  as  has  hap- 
pened in  the  case  of  the  Isle  of  Portland,  which  is 
now  connected  with  the  mainland  by  the  Chesil 
Beach. 

It  will  be  seen,  therefore,  that  if  conditions  remain 
uniform  the  tendency  of  the  onward  travel  of  shingle 
is  to  simplify  coast-lines  by  obliteration  of  the  in- 
dentations of  the  coast,  which  will  usually  be  found 
on  examination  to  owe  their  existence  to  subaerial 
denudation  followed  by  depression. 

Inspection  of  a  map  of  many  areas  shows  the 
frequent  tendency  of  the  coast-line  to  assume  the 
form  of  a  series  of  concave  curves  or  bays,  separated 
from  one  another  by  headlands  or  salient  points, 
which  are  often,  though  by  no  means  universally, 
formed  by  the  meeting  of  two  concave  curves.  If  we 


336     SCIENTIFIC   STUDY   OF   SCENERY 

examine  a  map  of  England,  we  shall  find  these  con- 
cave curves  on  a  large  scale,  usually  modified  by  the 
existence  of  minor  bays  along  the  line  of  each  larger 
one.  An  examination  of  the  geological  structure  of 
the  country  points  to  the  conclusion  that  the  larger 
bays  were  formed  when  the  area  was  at  a  different 
level  to  that  at  which  it  now  is,  but  this  is  a  point 
which  cannot  be  discussed  here.  The  concave  curve 
of  the  minor  bays  is  that  which  produces  so  very 
marked  an  influence  upon  the  scenery  of  many 
seaside  localities,  and  we  may  briefly  consider  the 
cause  of  these  concave  curves,  which  are  character- 
istic of  lake-shores,  as  shown  by  Gilbert,  as  well  as 
of  those  of  the  ocean. 

The  primary  cause  of  alternating  embayments 
and  salient  points  is  to  be  sought  for  by  an  ex- 
amination of  the  geological  structure  of  the  region 
adjoining  the  coast-line.  It  is  usually  found  that 
the  dominant  headlands  or  salient  points  owe  their 
existence  to  resistance  of  the  rocks  of  which  they 
are  composed  to  the  agents  of  erosion,  while  the 
embayments  are  marked  by  the  occurrence  of  more 
easily  eroded  rock  in  or  towards  the  centres. 
Thus  the  great  bay  which  extends  (modified  by 
many  a  minor  indentation)  from  Cumberland  to  the 
north  coast  of  Anglesea,  has  its  limiting  salients 
formed  in  the  durable  rocks  of  those  districts,  and 
the  centre  of  the  embayment  occurs  in  the  soft 
Triassic  rocks  of  Lancashire  and  Cheshire ;  the  bay 
extending  from  the  south  of  Carnarvonshire  to  Pem- 
brokeshire has  its  salients  formed  of  the  slaty  rocks 
which  are  associated  with  hard  igneous  rocks,  while 
the  centre  of  the  embayment  in  Cardigan  is  in  rocks 
which  are  not  penetrated  by  these  hard  igneous  ribs ; 


THE   OCEANS  337 

and,  to  give  one  more  example,  the  bay  between  the 
Start  and  the  Bill  of  Portland  has  its  salients  formed 
of  the  hard  Devonian  rocks  on  one  hand  and  the 
hard  Oolites  on  the  other,  while  the  centre  is  com- 
posed of  soft  Triassic,  Liassic,  and  Cretaceous  rocks. 

In  the  case  of  bays  formed  in  inland  lakes,  where 
the  power  of  the  waves  is  small  as  compared  with 
that  of  sea-waves,  the  formation  of  the  hollows  which 
ultimately  give  rise  to  bays  is  often  primarily  due  to 
subaerial  erosion  (a  point  which  should  be  taken  into 
account  when  considering  the  origin  of  lakes),  and 
this  is  the  case  to  some  extent  with  many  bays  along 
the  sea-coast,  though  here  the  action  of  the  waves  is 
often  sufficient  to  produce  marked  erosion  in  the 
centres  of  the  bays. 

On  a  small  scale,  as  has  already  been  seen,  the 
waves  of  the  sea  are  capable  of  fretting  the  coast 
into  irregular  shapes,  but  it  is  perfectly  clear  that  if 
a  soft  rock  coming  to  the  shore  as  a  narrow  strip  be 
worn  away,  a  time  must  come  when  the  indentation 
penetrates  so  far  inland  as  compared  with  its  width 
that  the  water  will  be  calm  even  during  storms,  and 
accordingly  the  erosion  is  checked,  until  the  harder 
rocks  on  either  side  are  worn  away  to  a  sufficient 
extent  to  allow  of  further  removal  of  the  soft  rock, 
and  beach  material  will  tend  to  accumulate  in  these 
hollowed-out  portions  ;  so  that  as  the  result  of  differen- 
tial wear  and  of  accumulation  in  places,  inequalities 
of  the  coast-line  gradually  disappear,  and  there  is 
a  tendency  to  development  of  a  regular  curved  outline 
between  the  salient  points.1 

1  In  some  cases  the  salient  points  are  replaced  by  convex  curves,  as, 
for  instance,  that  which  occurs  on  the  Norfolk  coast.     A  blunted  fore- 
land is  due  to  scour  off  the  original  point. 
Z 


338     SCIENTIFIC   STUDY   OF   SCENERY 

The  action  of  the  on-shore  currents  may  be  in 
many  ways  compared  with  that  of  a  river,  if  we 
compare  the  horizontal  action  of  the  former  with  the 
vertical  action  of  the  latter.  It  has  already  been 
remarked  that  in  some  cases  the  amount  of  shingle 
which  collects  on  a  foreshore  is  sufficient  to  check 
denudation,  and  there  must  be  a  point  where  neither 
denudation  of  the  land  nor  deposition  of  shingle  takes 
place.  Any  pre-existing  indentation  will  produce 
slack-water  and  cause  deposition  of  shingle,  while 
any  projection  will  tend  to  be  cut  away  and  recede 
backward,  until  eventually  a  marine  denudation  curve 
will  be  formed  by  deposition  in  embayments  and 
denudation  on  salient  points  until  equilibrium  is 
established.  The  curve  will  differ  from  the  denuda- 
tive curve  of  running  water,  in  being  horizontal 
instead  of  vertical,  and  will  sweep  from  one  salient 
point  to  another,  just  as  the  denudation  curve  sweeps 
from  ridge  to  ridge.1  In  rare  cases  the  conditions 
are  such  as  to  allow  of  the  growth  of  salient  points 
by  deposition.  They  are  spoken  of  as  "  cuspate  fore- 
lands," the  term  foreland  being  used  by  American 
geographers  to  denote  the  flat  ground  formed  by 
deposition  in  front  of  the  original  coast -line.  A 
good  example  of  such  a  cuspate  foreland  is  Dunge- 
ness,  which  has  been  described  by  Mr.  Cornish  and 
also  by  Dr.  T.  P.  Gulliver.2 

1  It  must  be  noted  that  the  existence  of  a  stable  beach  does  not 
imply  that  the  land  is  not  undergoing  denudation.     As  Mr.  Cornish 
observes,  "  The  erosion  of  the  sea-bottom  seaward  of  the  beach,  which 
is  really  a  slow  waste  of  the  land,  pushes  landward  the  proper  and 
stable  position  of  the  beach.     Thus,  unless  shingle  be  supplied  in  such 
quantity  as  to  produce  a  shingle  ness  or  foreland,  the  barrier  is  not 
fixed  in  position,  although  it  be  stable." 

2  GULLIVER,  T.  P.,  Geographical  Journal^  May,  1897. 


THE   OCEANS  339 

Should  a  coast  be  subjected  to  marine  action  with- 
out further  change,  the  salients  will  gradually  become 
eroded  and  the  embayments  filled,  and  the  curvature 
will  thereby  diminish,  until  a  state  of  equilibrium  is 
attained.  Before  this  equilibrium  has  been  attained 
it  will  be  approached  more  closely  when  other  con- 
ditions are  similar,  if  the  difference  of  hardness  of 
the  rocks  is  not  very  marked. 

In  a  country  like  our  own  additional  complication 
is  introduced  by  change  in  the  relative  level  of  land 
and  sea  in  comparatively  recent  times.  A  movement 
of  upheaval  will  give  rise  to  a  simple  coast-line 
formed  largely  of  sediment,  upon  which  denudation 
will  operate,  but  our  country  has  recently  undergone 
a  movement  of  depression,  and  this  renders  condi- 
tions much  more  complex.  Inequalities  have  been 
produced  by  subaerial  denudation,  and  the  hollows 
excavated  by  subaerial  agents  when  submerged  give 
rise  to  indentations  of  the  coast  which  are  occupied 
by  the  sea,  and  if  the  indentations  are  very  long  they 
may  exist  for  a  considerable  time  before  they  are 
destroyed  or  cut  off  by  the  formation  of  shingle 
barriers  across  the  mouths,  especially  if  the  water  is 
very  deep  at  the  mouth.  To  this  cause  we  owe  the 
great  indentation  of  our  western  coasts,  the  sea-lochs 
of  Scotland,  the  corresponding  loughs  of  Ireland, 
and  the  long,  winding  estuaries  of  Wales,  Devon,  and 
Cornwall ;  and  the  fjords  of  Norway  and  of  Green- 
land are  due  to  the  same  thing.  Many  of  our 
smaller  bays  which  occur  along  the  line  of  the  larger 
may  have  been  initiated  in  the  same  way. 

For  instance,  on  the  south-west  coast  of  Anglesea, 
which  forms  part  of  the  great  bay  between  Holyhead 
and  Bardsea  Island,  we  find  several  bays— Cymmeran 


340    SCIENTIFIC   STUDY   OF   SCENERY 

Bay,  Aberffraw  Bay,  Malldraeth  Bay,  and,  I  may  add, 
Carnarvon  Bay — which  at  present  present  the  normal 
concave  curve,  but  the  heads  are  filled  in  with  shingle 
banks,  blown  sand,  and  marsh  accumulation,  and  the 
outline  of  the  original  land  is  so  irregular  that  it 
seems  almost  certain  that  it  owes  its  origin  to  sub- 
aerial  action,  while  in  each  case  an  important  river 
runs  into  the  bay  (except  in  Carnarvon  Bay,  where 
the  former  river  is  now  occupied  by  the  south-western 
part  of  the  Menai  Straits).1 

A  few  words  concerning  the  formation  of  sand- 
banks may  be  of  interest  on  account  of  the  import- 
ance which  they  play  upon  the  scenery  of  a  coast  at 
sunrise  and  sunset.  The  condition  under  which  sand 
is  deposited  has  already  been  briefly  noted.  Tidal 
movement  produces  a  series  of  vibrating  segments  of 
water,  which  Mr.  Cornish  believes  to  be  elongated 
ellipses,  and  nodes  occur  between  the  segments  along 
which  sand  is  deposited,  especially  along  those  nodes 
which  separate  the  ellipses  and  lie  parallel  with  their 
longer  axes,  thus  producing  longitudinal  sandbanks. 

1  The  origin  of  fjords  is  now  generally  admitted  to  be  due  to  occu- 
pation by  the  sea  of  hollows  originally  formed  by  subaerial  erosion. 
Various  explanations  have  been  offered  to  account  for  the  original 
formation  of  the  hollows,  but  any  cause  which  produces  a  hollow  on 
the  land  will  naturally  give  rise  to  an  indentation  of  the  coast-line 
when  that  hollow  is  occupied  by  the  sea.  Professor  Brogger  has 
written  an  elaborate  paper  on  the  Christiania  Fjord  {Nyt  Migazin  for 
Naturvidenskabeme,  1886)  in  which  he  shows  that  the  fjord  lies  in  a 
broken  anticline,  affected  by  faults,  which  have  let  down  softer  rocks 
against  harder  ones,  and  that  the  softer  rocks  have  been  eroded  by  sub- 
aerial  agencies  in  such  a  way  that  the  major  lines  of  the  fjord  coin- 
cide closely  with  the  major  faults,  and  in  many  cases  the  minor  lines 
similarly  coincide  with  minor  faults.  The  same  thing  is  observable  to 
some  extent  on  the  north  shore  of  Morecambe  Bay  with  its  estuaries. 
The  coast-lines  of  the  fjords  of  Western  Greenland  have  been  largely 
determined  by  erosion  along  the  major  joint-planes. 


THE   OCEANS  341 

"  Such  are  the  sandbanks  parallel  to  the  shore,  which 
are  numerous  off  the  coasts  from  Flamborough  Head 
to  the  South  Foreland,  and  from  Calais,  at  least,  as 
far  as  the  Zuyder  Zee.  These  sandbanks  are  parallel 
to  the  main  run  of  the  along-shore  tidal  currents." 
Other  sandbanks  are  formed  on  the  lee  side  of  head- 
lands, "  of  which  the  Skerries  shoal,  eastward  of  Start 
Point,  and  the  Shambles  shoal,  eastward  of  Port- 
land Bill,"  are  examples.  Mr.  Cornish  terms  these 
"banner  sandbanks,"  inasmuch  as  they  resemble 
cloud-banners  in  being  formed  by  a  moving  current, 
their  permanence  being  due  to  fresh  supply  of  sand 
to  compensate  for  the  loss.  Sand-bars  off  river- 
mouths  are  usually  stated  to  be  due  to  the  checking 
of  the  river  -  current  when  it  enters  the  sea,  but 
Mr.  Cornish  gives  reasons  for  supposing  that  the 
action  is  not  quite  so  simple,  and  is  probably  due 
to  the  motions  which  attend  the  mixing  of  the 
waters. 

Hitherto  we  have  considered  chiefly  the  action  of 
the  sea  along  the  actual  shore-line,  though  we  have 
noted  that  there  is  erosion  on  the  seaward  side  of 
the  beach  accumulations.  It  has  already  been  stated 
that  the  downward  trend  of  this  erosion  is  limited  by 
the  depth  at  which  wave-action  is  efficacious  as  an 
agent  of  erosion,  and  that  this  depth  is  slight, 
although  it  probably  varies  somewhat  according  to 
the  character  of  the  waves.  As  the  variations  will 
not  be  great  in  the  same  locality,  the  ultimate  result 
of  marine  erosion  as  the  sea  encroaches  upon  the 
land  will  be  to  reduce  the  destroyed  land  to  the 
level  at  which  the  waves  cannot  any  longer  exert  an 
erosive  influence,  that  is  to  a  level  of  at  most  a  few 
score  fathoms  below  the  ocean  surface.  Such  a 


342     SCIENTIFIC   STUDY   OF   SCENERY 

levelled  tract  is  known  as  a  plain  of  marine  denuda- 
tion, and  its  importance  is  well  known  to  the  geologist. 
To  us  it  is  important,  because  if  upheaved  by  a  gentle 
and  extensive  uplift  it  will  give  rise  to  a  continental 
plain,  thus  adding  another  and  very  important  cause 
to  those  which  we  have  already  considered  as  respon- 
sible for  the  formation  of  plains. 

It  has  already  been  noted  that  the  marine  deposits 
when  laid  down,  present  a  fairly  level  upper  surface, 
which  may  be  spoken  of  as  a  plain  of  marine  deposi- 
tion, and  the  upheaval  of  these  plains  of  deposit 
furnishes  yet  another  class  of  continental  plains. 

Oceanic  Islands. — Islands  are  produced  in  the  ocean 
in  various  ways.  Many  of  them  were  originally 
portions  of  continents  which  have  been  separated 
at  different  times  as  the  result  of  denudation  or  of 
depression  of  intervening  tracts,  or  by  a  combination 
of  the  two  processes.  Others  are  due  to  upheaval 
of  parts  of  the  sea-floor,  which,  if  continued,  may 
result  in  the  coalescence  of  the  island  with  an  adjoin- 
ing continent.  Others,  again,  are  due  to  accumu- 
lation, either  of  detrital  material  derived  from  the 
denudation  of  continents,  or  of  volcanic  matter,  or 
of  the  hard  parts  of  organisms. 

Islands  which  have  been  separated  from  the 
continents  present  the  same  features  of  coast-line 
as  do  the  continental  tracts.  An  island,  like  a  con- 
tinent, when  undergoing  submergence,  is  marked  by 
fjord-like  indentations  of  the  coast-line,  if  the  original 
slopes  were  steep.  In  this  way  has  been  produced 
the  very  remarkable  shape  of  the  island  of  Celebes, 
which  is  the  relic  of  a  mass  of  land  of  greater 
extent,  much  of  which  has  been  submerged. 

Islands  formed  by  upheaval  are  frequently  found 


THE   OCEANS 


343 


along  lines  of  uplift,  and  run  in  linear  groups,  the 
line  being  often  a  curved  one,  with  the  concavity 
facing  an  adjoining  continent.  Such  islands  are 
known  as  festoon  islands,  and  are  the  tops  of  uplifts, 
which  as  the  process  is  continued  may  give  rise  to 
a  continuous  tract  of  land,  and  finally  may  be  added 
to  the  adjoining  continent.  Examples  of  festoon 
islands  are  furnished  by  the  West  Indies  and  Japan 
and  Sagalien  Island. 

Those  islands  which  are  formed  by  deposit  of 
material  derived  from  denudation  of  the  land  are 
usually  low-lying,  and  are  readily  destroyed  when 
conditions  change,  allowing  of  denudation  to  take 
place  where  deposition  occurred  previously.  From 
a  scenic  point  of  view  they  are  of  little  interest. 

Islands  which  are  wholly  composed  of  volcanic 
rocks  commence  as  submarine  shoals,  and  if  the 
action  of  the  waves  is  not  sufficiently  strong  to 
check  the  growth  of  the  volcano  above  the  water 
an  island  is  formed.  A  large  number  of  oceanic 
islands  are  of  volcanic  origin.  When  a  volcanic 
island  has  been  affected  by  paroxysmal  eruptions, 
which  have  reduced  the  lower  part  of  the  crater  to 
a  depth  below  sea-level,  and  the  sea  has  communica- 
tion with  the  interior,  we  may  have  an  island  with 
a  central  lagoon  of  water  communicating  with  the 
ocean  by  one  channel,  as  was  once,  though  erroneously, 
stated  to  be  the  case  with  Barren  Island  in  the  Bay 
of  Bengal ;  the  Lago  del  Bagno  in  Ischia  fills  an  old 
crater,  and  has  been  converted  into  a  harbour,  but  by 
artificial  means.  Other  craters  which  are  filled  by 
the  sea  open  to  the  ocean  by  several  passages,  for 
the  old  crater-ring  has  had  gaps  formed  in  various 
places.  Thus  the  Archipelago  of  Santorin  in  the 


344    SCIENTIFIC   STUDY   OF  SCENERY 

Eastern  Mediterranean  consists  of  the  three  islands 
Thera,  Therasia  and  Aspronisi,  enclosing  a  roughly 
circular  lagoon,  in  the  centre  of  which  rise  the  small 
Kaimenis,  islands  formed  by  minor  cones  in  the 
middle  of  the  ancient  truncated  cone,  and  Krakatoa 
forms  a  similar  ring,  consisting  of  the  main  island 
and  Verlaten  and  Lang  Islands. 

There  remain  the  coral  islands,  which  have  always 
exercised  a  fascination  in  the  minds  of  travellers  and 
those  who  are  interested  in  scenery,  on  account  of 
their  nature  and  surroundings,  and  much  attention 
has  been  directed  to  them  during  recent  years,  on 
account  of  the  discussion  which  has  arisen  concerning 
their  origin.  It  is  unnecessary  to  enter  into  any 
detail  concerning  this  discussion  in  a  work  like  the 
present,  all  that  we  can  do  is  to  note  the  general 
characters  of  coral  reefs,  and  briefly  allude  to  their 
formation.  It  is  well  known  that  three  kinds  of 
reef  are  found,  which  differ  in  their  character. 
Fringing  reefs  consist  of  a  fringe  of  organically- 
formed  limestone,  adhering  to  the  side  of  an  island 
usually  composed  of  volcanic  rock.  Barrier  reefs, 
or  encircling  reefs  as  those  which  encircle  an  island 
are  termed,  may  extend  along  part  of  a  continental 
mass,  as  the  Great  Barrier  Reef  which  runs  for  iioo 
miles  off  the  north  coast  of  Australia,  or  may  surround, 
or  partly  surround,  an  island.  They  are  characterised 
by  the  existence  of  a  tract  of  water  often  of  con- 
siderable depth  lying  between  them  and  the  land 
to  which  they  form  a  barrier ;  when  this  is  an  island 
the  water  between  the  barrier  and  the  island  forms 
a  lagoon.  Lastly  atolls  are  ring-shaped  masses  of 
coral  surrounding  a  lagoon,  with  no  island  in  the 
centre  of  the  lagoon.  The  ring  may  be,  and  often 


THE   OCEANS  345 

is,  very  irregular,  and  though  frequently  approaching 
the  form  of  a  circle,  often  approximates  to  that  of 
an  ellipse.  These  coral-reefs  are  found  only  in  clear 
seas,  and  in  tropical  or  sub-tropical  regions,  and  the 
fact  that  the  distribution  of  reef-building  corals  is 
limited  by  temperature  is  further  proved  by  the 
discovery  that  reef-building  corals  have  a  vertical 
limit;  it  was  formerly  stated  that  they  could  not 
flourish  at  a  depth  exceeding  thirty  fathoms,  but 
they  have  been  found  at  a  greater  depth,  and  their 
exact  downward  limit  seems  to  be  still  undetermined.1 

The  rim  of  rock  which  forms  the  foundation  of 
the  island,  and  lies  below  high-water  mark,  is  largely 
composed  of  various  kinds  of  corals,  both  massive 
and  branching,  but  calcareous  nullipores  also  con- 
tribute very  largely  to  its  substance  in  many  places. 
The  actual  islands,  which  lie  on  this  submarine 
foundation,  are  composed  of  fragments  piled  up  by 
the  waves  to  form  a  beach,  and  cemented  owing  to 
the  solvent  action  of  percolating  water.  Between  the 
islands  are  usually  a  number  of  passages,  in  the 
case  of  barrier  reefs  and  atolls,  which  connect  the 
lagoon  with  the  open  ocean.  At  low  water  con- 
siderable tracts  of  coral-rock  with  a  flat  surface  are 
often  exposed  and  extend  some  way  seawards ;  they 
are  usually  terminated  by  very  steep  slopes,  often 
extending  downwards  to  great  depths. 

As  these  coral  islands  often  rise  from  very  deep 

1  The  structure  and  characters  of  coral-reefs  are  described  in 
DARWIN'S  Coral  Reefs  and  J.  D.  DANA'S  Corals  and  Coral  Islands  ; 
'beautiful  illustrations  of  the  appearance  of  coral-reefs  accompany 
Mr.  Savile  Kent's  work  on  the  Great  Barrier  Reef;  and  an  account  of 
Sir  J.  Murray's  views  will  be  found  in  a  paper  by  him  in  Nature, 
vol.  xxii.,  p.  351. 


346     SCIENTIFIC   STUDY   OF  SCENERY 

parts  of  the  ocean,  and  as  the  reef-forming  coral  has 
a  downward  limit  not  far  removed  from  the  surface, 
it  becomes  of  importance  to  determine  how  the 
islands  were  formed.  According  to  Darwin,  atolls 
usually  commenced  as  fringing  reefs,  and  owing  to 
depression  of  the  island,  and  the  building  up  of  the 
corals  in  a  nearly  vertical  direction,  the  outer  margin 
of  the  reef  gradually  grew  away  from  the  island, 
and  owing  to  the  unfavourable  state  of  the  inner 
part  of  the  reef  for  coral-growth,  a  lagoon  was 
formed.  When  the  island  in  the  lagoon  finally  sank 
the  barrier  reef  was  converted  into  an  atoll.  Sir  J. 
Murray,  on  the  other  hand,  supposes  that  submarine 
platforms  are  raised  by  volcanic  action  and  the 
accumulation  of  the  tests  of  pelagic  organisms  floating 
in  the  upper  waters  of  the  ocean  to  the  height  of 
the  downward  limit  of  coral  formation,  when  corals 
begin  to  build  reefs.  The  inner  portions  of  these 
reefs  will  be  unfavourable  to  coral  growth,  and  owing 
to  this  and  to  solution  a  lagoon  will  be  formed. 
Fragments  broken  off  by  the  waves  will  roll  down 
the  outer  slope  and  raise  portions  of  it  to  the 
requisite  height  for  coral-growth,  and  the  reef- 
forming  corals  will  extend  outwards  upon  this 
raised  portion.  Thus  Murray  considers  that  the 
atoll  does  not  grow  from  a  barrier  reef,  but  practically 
commences  as  an  atoll,  and  that  as  the  outer  part  of 
the  reef  expands  outwards  on  the  fallen  blocks,  the 
lagoon  also  expands  by  solution — in  fact  that  an  atoll 
commences  as  a  small  ring,  which  gradually  grows 
in  diameter,  the  width  of  the  actual  islets  practically 
remaining  constant  during  the  process.  It  must  be' 
noted  that  Darwin  actually  took  into  consideration 
this  mode  of  formation  of  atolls,  and  rejected  it  as 


THE   OCEANS  347 

inapplicable  to  the  larger  number  of  atolls  on  account 
of  what  he  conceived  to  be  the  improbability  of  the 
formation  of  the  requisite  number  of  submarine 
platforms  raised  to  the  required  height  without 
emerging  to  the  surface  of  the  ocean.  The  relative 
applicability  of  the  two  theories  to  explain  atoll 
formation  is  a  matter  which  is  still  sub  judice,  but 
the  words  of  Professor  Huxley,  quoted  by  Professor 
Judd,  in  a  discussion  to  a  recent  paper  at  the 
Geographical  Society,  probably  express  the  truth  of 
the  matter.  Professor  Judd  remarked  that  he  had 
been  discussing  the  question  with  Professor  Huxley, 
and  that  the  latter  observed,  "  I  am  convinced,  from 
all  that  is  being  done  now,  that  we  shall  not  find 
any  simple,  easy  explanation  of  all  coral-reefs ;  that 
the  study  of  coral-reefs  is  one  of  the  very  greatest 
complexity ;  that  the  conditions  under  which  they 
were  formed  would  have  varied  greatly  in  different 
cases ;  and  that  one  theory  of  their  origin  will 
probably  not  be  found  to  suit  all  the  cases " ;  and, 
adds  Professor  Judd,  "  I  think  that  the  experience 
of  the  last  few  years  will  tend  to  convince  everyone 
of  the  truth  of  this  observation." 

The  peculiar  scenery  of  a  coral-reef  encircling  a 
lagoon  is  dependent  upon  the  dazzling  whiteness  of 
the  beach,  formed  of  broken  calcareous  fragments, 
upon  the  contrast  between  the  still  waters  of  the 
lagoon  and  the  surge  which  breaks  on  the  outer  part 
of  the  reef,  and  upon  the  character  of  the  vegetation, 
which  soon  springs  up,  owing  to  the  seeds  trans- 
ported by  the  ocean,  or  probably  more  frequently 
by  birds,  which  germinate,  and  grow  into  plants 
which  gradually  give  rise  to  a  soil  capable  of 
supporting  the  luxuriant  vegetation  which  is  so 


348     SCIENTIFIC   STUDY   OF   SCENERY 

frequently  met  with  on,  and  forms  so  marked  a 
character  of,  these  coral  islets. 

Raised  Sea-Margins. — As  the  result  of  uplift,  or 
it  may  be  in  some  cases  of  the  retirement  of  the 
sea,  the  features  which  were  noticed  in  the  last 
chapter  as  characteristic  of  the  action  of  the  sea 
along  the  sea-coast,  are  often  found  some  distance 
inland.  We  meet  with  raised  sea-cliffs,  frequently 
pierced  by  sea-caverns,  and  in  other  places  with 
raised  beaches.  Each  of  these  often  forms  a  marked 
feature  in  the  scenery  of  a  district.  Beginning  with 
the  cliffs  —  raised  cliffs  may  be  found  on  many 
parts  of  our  coast,  especially  on  the  western  side, 
far  removed  from  the  wash  of  the  waves  of  the 
present  ocean.  They  are  frequently  separated  from 
the  present  cliff  by  a  nearly  flat  or  gently  sloping 
terrace,  which  may  be  a  plain  of  marine  denudation, 
or  a  plain  of  deposition,  or  one  due  to  the  deposition 
of  a  thin  deposit  of  sediment  upon  a  plain  of  denu- 
dation. Of  this  nature  are  many  of  the  carses  of 
Scotland,  well  seen  along  the  estuary  of  the  Clyde, 
and  frequently  backed  by  the  old  sea-cliffs.  When 
surrounding  an  island  these  carses  give  the  isle  a 
very  characteristic  appearance,  the  raised  interior 
being  surrounded  by  a  low,  flat  terrace  standing 
above  a  small  modern  cliff,  as  in  the  case  of  Great 
and  Little  Cumbrae,  on  the  Clyde  estuary.  Among 
coral  islands  raised  reefs  often  take  the  place  of  the 
sea-cliffs,  and  the  ancient  lagoon  may  be  formed  on 
the  landward  side  of  these  reefs  as  a  depression, 
as  recently  described  by  Mr.  Andrews  in  the  case 
of  Christmas  Island.1 

Raised  beaches  are  very  frequent,  and  often  give 
1  ANDREWS,  C.  W.,  Geographical  Journal,  loe.  cit. 


THE   OCEANS  349 

rise  to  terraced  lines,  resembling  in  general  aspect 
those  Parallel  Roads  of  Glenroy  to  which  reference 
has  been  already  made.  They  are  frequent  along 
the  coast  of  Scotland,  often  rising  terrace  above 
terrace  to  heights  of  100  feet  above  present  sea-level. 
In  Norway  they  are  frequently  seen  running  in 
parallel  lines  around  the  fjords,  and  a  magnificent 
series  of  terraces  is  found  surrounding  the  shores  of 
the  White  Sea.  Some  of  the  most  remarkable  of 
these  terraces  exist  in  South  America,  where  they 
have  been  very  fully  described  by  Darwin.1  They 
occur,  with  well-marked  features,  to  heights  of  over 
300  feet  above  sea-level,  and  have  been  found  at 
intervals  along  the  Atlantic  coast  from  Tierra  del 
Fuego  for  a  distance  of  1180  miles  northward,  and 
along  the  Pacific  coast  have  been  traced  for  a  distance 
of  2075  miles.  For  a  length  of  775  miles  they  occur 
on  both  sides  of  the  Continent  in  the  same  latitude. 
In  Greenland,  again,  these  raised  beaches  have  been 
described  on  the  western  coast,  and  they  are  also 
found  in  New  Zealand  and  in  many  other  areas. 

Marine  Vegetation. — The  marine  algae,  which  have 
a  prevalent  olive-brown  or  olive-green  hue,  though 
many  are  red  or  violet,  often  produce  a  considerable 
effect  upon  marine  scenery.  At  low  water  our  shores 
are  often  seen  to  be  densely  clad  with  masses  of 
algae,  and  they  may  be  seen  waving  on  the  shallows 
when  a  boat  passes  over  them,  many  of  them  being 
buoyed  up  by  the  vesicles  which  they  possess.  In 
the  southern  polar  seas  grows  the  gigantic  Macro- 
cystis  pyrifera,  which  sometimes  attains  a  length  of 
over  500  yards. 

In  addition  to  the  algae  found  around  the  coasts, 

1  Geological  Observations^  p.  232. 


350    SCIENTIFIC   STUDY   OF   SCENERY 

attached  to  the  sea-bottom,  are  others  which  float 
freely  in  the  water,  as  the  well-known  Sargassum 
bacciferum,  or  gulf-weed,  of  which  detached  masses 
cover  thousands  of  square  miles  of  the  oceans  in 
those  great  central  "whirls"  of  quiet  water  which  lie 
inside,  and  are  due  to  the  circulating  masses  of 
oceanic  water  which,  in  the  northern  hemisphere, 
move  in  the  direction  of  the  hands  of  a  clock,  and 
in  the  southern  hemisphere  in  the  contrary  direction. 
The  best  known  of  these  areas  is  the  Sargasso  Sea, 
in  the  North  Atlantic,  though  similar  accumulations 
of  "weed"  and  other  flotsam  are  also  formed  in 
the  Pacific  Ocean,  and  form  the  home  of  countless 
animals,  some  of  which  are  attached  to  the  "  weed," 
while  others  float  and  swim  among  it. 

Ice  in  the  Ocean. — We  have  already  considered  the 
mode  of  formation  of  icebergs,  and  made  brief  allu- 
sion to  the  pack-ice  of  Spitsbergen,  but  it  yet  remains 
to  make  a  few  remarks  concerning  this  ice  and  its 
formation.  The  water  on  the  coasts  of  Arctic 
regions  freezes  in  winter,  and  forms  a  coating  at- 
tached to  the  coasts  known  as  coast-ice.  It  forms 
on  the  surface  and  beneath,  and  often  attains  a  great 
thickness.  Material  falls  on  to  it  from  cliffs,  and  is 
frozen  into  it  when  it  forms  against  beaches,  and 
when  the  ice  breaks  up  in  spring  it  floats  away,  trans- 
porting this  material  and  depositing  it  elsewhere. 

Further,  the  whole  surface  of  great  tracts  of  the 
ocean  freezes  in  the  winter  in  Arctic  regions,  and 
breaks  up  on  the  approach  of  summer  along  exten- 
sive lines  of  fissure,  the  detached  portions  floating  off 
as  ice-floes.  These  floes  are  often  formed  of  great 
sheets  of  ice  reared  up  edgewise,  and  piled  up  one 
on  the  top  of  the  other  to  form  pack-ice.  It  is  this 


THE   OCEANS  351 

pack-ice  which,  forced  through  the  narrow  straits  of 
Spitsbergen  and  elsewhere  by  currents  and  races  of 
great  velocity,  and  often  of  considerable  constancy 
of  direction,  gives  rise  to  those  rounded  and  striated 
rocks  which,  in  the  present  state  of  our  knowledge, 
it  is  difficult,  if  not  impossible,  to  distinguish  from 
the  rounded,  smoothed,  and  striated  rocks  which  have 
acquired  their  present  shape  as  the  result  of  the 
action  of  land-ice. 


CHAPTER  XX. 
CONCLUSION 

AN  attempt  has  been  made  in  the  foregoing 
chapters  to  show  that  the  various  scenic 
features  of  the  earth's  surface  were  produced  by  the 
operation  of  agents,  whose  mode  of  action  is  familiar 
to  us.  We  need  not  invoke  the  aid  of  any 
mysterious  force,  in  order  to  account  for  these 
features ;  allow  a  sufficient  amount  of  time,  and  the 
sea  will  receive  enough  sediment  to  supply  material 
for  the  formation  of  fresh  continents,  the  forces 
which  are  at  work  on  the  earth's  interior  will  elevate 
these  sediments  above  the  level  of  the  sea,  convert- 
ing them  into  dry  land,  and  the  incessant  action  of 
the  sculpturing  tools,  of  wind,  rain,  frost,  rivers, 
glaciers,  sea-waves,  and  the  like,  will  carve  out  the 
continents  into  those  shapes  whose  origin  it  has 
been  our  task  to  consider.  The  nature  of  these 
changes  and  their  effects  are  so  clearly  understood 
that  they  have  become  the  ^very  alphabet  of  modern 
geological  science,  but  there  is  yet  much  work  to 
be  done  in  working  out  the  details,  and  also  in 
discussing  the  causes  of  many  of  the  changes. 

As  the  student   of  scenery  pursues   his  inquiries 

into  the  origin  of  the  earth's  features,  he  will  find 

that    he    is    led    into    many    by-paths,    of    whose 

existence    he    was    previously    unaware.     Roaming 

352 


CONCLUSION  353 

among  the  sand-dunes  of  the  coast,  he  is  first  led 
to  inquire  how  the  sand  was  heaped  up  to  form 
the  crescentic  ridges,  but  when  he  has  done  this  he 
will  not  be  content  until  he  has  gained  some  know- 
ledge of  the  history  of  the  individual  sand-grains, 
and  here  he  will  find  a  story  so  strange  that  it  seems 
at  first  well  nigh  incredible.  The  grain  was  perhaps 
brought  into  existence  as  a  grain  long,  long  ages 
ago,  upon  the  consolidation  of  a  mass  of  molten 
rock  deep  down  within  the  bowels  of  the  earth. 
The  crystalline  forces  which  called  it  into  being 
were  capable  of  giving  it  a  shape  as  definite  as  the 
form  of  a  living  organism,  but  the  conditions  were 
perhaps  unfavourable  for  the  assumption  of  that 
shape.  Ages  roll  by,  and  the  grain  is  locked  up 
in  the  earth's  interior,  until  the  slow  upheaval  of 
part  of  the  crust,  and  the  removal  by  denudation 
of  the  exterior  of  that  crust,  expose  it  upon  the 
surface.  Acidulated  water  may  corrode  it,  fragments 
of  it  may  be  chipped  off  during  its  passage  down 
some  river  to  the  sea,  and  it  may  be  deposited  in 
its  altered  form  at  the  sea-bottom,  perhaps  to  be 
uplifted  and  again  denuded  time  after  time.  In  its 
present  state  on  the  dune  it  may  become  rounded 
by  friction  against  other  grains  when  blown  along 
by  the  wind,  until  it  has  been  materially  reduced 
in  size.  We  can  destroy  it  now,  as  a  grain  of  sand, 
by  immersing  it  in  an  acid  which  will  dissolve  silica 
— it  would  be  killed — but  if  we  do  not  thus  destroy 
it  the  crystalline  forces  which  called  it  into  existence 
may  act  upon  it  at  some  future  time  under  circum- 
stances favourable  to  its  completion  as  a  crystal  of 
definite  outline.  After  long  ages  of  unfavourable 
existence  it  will  then  have  attained  its  full  growth, 


354    SCIENTIFIC   STUDY   OF   SCENERY 

and  its  decay  may  be  prolonged  through  ages  as  vast 
as  those  which  have  been  required  for  its  growth. 
There  are  thus  many  analogies  between  the  growth 
and  decay  of  a  crystal  and  the  growth  and  decay 
of  an  organism  ;  but  how  insignificant  is  the  period 
of  duration  of  the  organism  as  compared  with  that 
of  the  crystal !  Another  grain  we  may  discover 
composed  of  a  fragment  of  an  organism,  or  fragments 
of  many  organisms,  and  we  are  thus  led  to  inquire 
into  the  life  of  the  globe  in  past  times.  We  may 
discover  that  the  apparently  structureless  limestone 
which,  after  accumulating  to  a  thickness  of  thousands 
of  feet  on  the  ocean  floor,  has  been  reared  up  and 
sculptured  into  mighty  hills  and  strange  pinnacles, 
is  a  mosaic  composed  of  particles  so  small  that  they 
can  only  be  seen  beneath  the  microscope,  and  yet 
each  particle  consists  of  the  exquisitely  ornate  shell 
of  a  lovely  creature  which  once  existed  in  a  long- 
departed  ocean.  We  thus  learn  that  the  present 
earth-features  are  but  records  of  a  brief  period  ;  that 
past  periods  have  succeeded  one  another  before  the 
present,  each  marked  by  features  of  the  earth's 
surface,  in  many  respects  similar  to  those  which  are 
at  present  in  being,  but  each  probably  characterised 
by  something  belonging  to  the  period,  which  never 
occurred  before  and  will  never  occur  again.  One  is 
thus  led  to  pass  in  review  in  one's  imagination  the 
whole  of  the  earth's  history,  from  the  time  when 
the  earth  was  a  formless  nebula,  to  a  later  period 
when  it  was  a  molten  mass ;  yet  later,  when,  though 
solid,  it  was  a  lifeless  desert ;  and  so  through  the  long 
ages  of  geological  time  until  one  arrives  at  the 
contemplation  of  the  present  condition  of  things. 
And  the  future?  The  geologist  has  no  direct 


CONCLUSION  355 

evidence  of  the  beginning  of  things.  When  the  first 
sediments  of  which  we  have  any  certain  knowledge 
were  deposited,  the  condition  of  the  earth  had  in 
many  ways  approximated  so  nearly  to  existing  con- 
ditions that  we  feel  that  the  time  that  had  elapsed 
before  this  was  enormous  as  compared  with  the  time 
which  has  since  passed  by,  vast  as  this  must  be. 
And,  as  the  geologist  has  no  direct  knowledge  of 
the  beginning  of  things,  he  sees  no  signs  of  an 
approaching  end;  he  turns  to  the  physicist  and 
astronomer  for  information  of  the  death  of  the  earth 
as  of  its  birth.  But  he  sees  no  reason  for  supposing 
that  that  death  is  imminent ;  the  earth's  surface  may 
be  sculptured  and  upheaved  through  long  aeons  of 
time  to  come  before  the  end. 

But  let  us  leave  this  subject  of  geological  time, 
a  subject  so  awe-inspiring  that  the  brain  reels  when 
contemplating  it  too  closely,  and  turn  to  take  a  last 
look  at  the  condition  of  things  as  they  now  are. 

We  have  noted  a  difference  in  the  operation  of  the 
dominant  agents  which  give  rise  to  the  varied  scenic 
features  of  the  earth's  surface,  when  we  study  different 
parts  of  the  earth's  surface.  The  desert,  the  sea- 
coast,  the  arctic  uplands,  the  river-plain,  each  has  its 
own  particular  features.  Now  some  of  these  features 
are  due  to  climatic  conditions,  and  we  accordingly 
find  definite  types  of  scenery  which  are  apt  to  occur 
in  similar  latitudes.  We  may  divide  the  earth's 
surface  into  seven  belts,  namely,  the  tropical  belt,  the 
north  and  south  sub-tropical  belts,  the  north  and  south 
temperate  belts,  and  the  arctic  and  antarctic  belts. 

Commencing  with  the  tropical  belt,  we  find  that 
its  characteristic  features  are  largely  dependent  upon 
the  excessive  rainfall,  which  is  due  to  the  great 


356     SCIENTIFIC   STUDY   OF   SCENERY 

evaporation  caused  by  the  sun's  heat  in  equatorial 
regions.  This  rainfall,  combined  with  the  heat,  is 
favourable  for  the  growth  of  luxuriant  vegetation, 
and  accordingly  the  tropical  zone  is  specially  marked 
by  its  extensive  forests,  and  these  in  turn,  for  reasons 
which  we  have  already  given,  tend  to  produce  a 
certain  sameness  of  outline  in  the  country,  which  is 
not  greatly  diversified  by  the  work  of  erosive  agents, 
as  is  the  case  with  countries  which  are  not  so 
extensively  covered  with  vegetation. 

Many  people  have  exaggerated  ideas  of  the  beauty 
of  tropical  vegetation,  and  I  am  tempted  to  quote 
Mr.  A.  R.  Wallace's  descriptions  of  the  tropical 
forests  of  South  America  :l  "The  beauty  of  the  palm- 
trees  can  scarcely  be  too  highly  drawn  ;  they  are 
peculiarly  characteristic  of  the  tropics,  and  their 
varied  and  elegant  forms,  their  beautiful  foliage,  and 
their  fruits  ....  give  them  a  never-failing  interest 
to  the  naturalist,  and  to  all  who  are  familiar  with 
descriptions  of  the  countries  where  they  most  abound. 
The  rest  of  the  vegetation  was  hardly  what  I 
expected.  We  found  many  beautiful  flowers  and 
climbing  plants,  but  there  are  also  many  places  which 
are  just  as  weedy  in  their  appearance  as  in  our  own 
bleak  climate."  And  again,  "  A  few  forest  trees  were 
....  in  blossom  ;  and  it  was  a  truly  magnificent 
sight  to  behold  a  great  tree  covered  with  one  mass  of 
flowers,  and  to  hear  the  deep,  distant  hum  of  millions 
of  insects  gathered  together  to  enjoy  the  honeyed 
feast.  But  all  is  out  of  reach  of  the  curious  and 
admiring  naturalist.  It  is  only  over  the  outside  of 
the  great  dome  of  verdure  exposed  to  the  vertical 
rays  of  the  sun  that  flowers  are  produced,  and  on 

1  WALLACE,  A.  R.,  Travels  on  the  Amazon,  chaps,  i.  and  ii. 


CONCLUSION  357 

many  of  these  trees  there  is  not  a  single  blossom  to 
be  found  at  a  less  height  than  a  hundred  feet.  The 
whole  glory  of  these  forests  could  only  be  seen  by 
sailing  gently  in  a  balloon  over  the  undulating 
flowery  surface  above;  such  a  treat  is  perhaps  re- 
served for  the  traveller  of  a  future  age." 

It  is  in  the  sub-tropical  belts,  as  has  already  been 
stated,  that  the  main  deserts  of  the  earth's  surface 
occur,  and  present  characters  which  have  been  con- 
sidered in  the  chapter  devoted  to  the  desert-regions. 
It  is  not  to  be  supposed  that  the  whole  of  the 
sub-tropical  regions  are  occupied  by  desert,  any  more 
than  that  the  whole  of  the  tropical  belt  is  covered  by 
forest-growth,  but  when  the  physical  conditions  are 
such  as  are  necessary  for  the  existence  of  deserts, 
the  sub -tropical  climate  specially  favours  desert 
formation. 

In  these  desert  regions,  the  operation  of  agents  in 
a  dry  way  is  very  marked,  and  the  scenic  features  are 
largely  due  to  change  of  temperature,  and  the  action 
of  wind. 

In  the  temperate  belts,  the  climate  is  of  a  nature 
specially  suited  for  cultivation,  and  accordingly  it  is  in 
these  regions  that  man  has  most  thickly  congregated, 
and  has  produced  most  influence  upon  the  scenery 
of  the  earth's  surface,  owing  to  the  modifications 
brought  about  by  his  labours.  In  these  belts,  owing 
to  the  abundant  rainfall,  denudation  is  usually  carried 
on  in  the  wet  way,  especially  by  streams  and  rivers, 
but,  owing  to  the  less  dense  growth  of  vegetation,  as 
compared  with  that  of  tropical  regions,  the  effect  of 
denudation  is  to  produce  greater  superficial  inequali- 
ties than  those  which  are  carved  out  in  the  forest- 
clad  belt  on  either  side  of  the  equator. 


358     SCIENTIFIC    STUDY   OF   SCENERY 

In  the  arctic  and  antarctic  regions,  the  scenery  is 
essentially  affected,  so  far  as  sculpture  is  concerned, 
by  the  action  of  frost.  It  is  in  these  regions  that  the 
house-roof  type  of  mountain  with  straight  sides  is 
carved  out  with  greatest  frequency. 

The  above  remarks  concerning  the  influence  of 
climate  have  been  inserted,  because  we  are  too  prone 
to  consider  the  physical  features  of  our  own  area 
to  be  typical  of  those  which  are  found  elsewhere, 
and  to  overlook  the  fact  that  climatic  conditions 
play  so  important  a  role  in  the  production  of  scenic 
features  that  different  belts  of  the  earth's  surface 
have  different  kinds  of  scenery,  partly  due  directly 
to  difference  in  the  character  of  the  vegetation,  and 
partly  indirectly  to  the  same  difference,  but  partly 
also  to  the  difference  in  the  relative  importance  of 
the  different  denuding  agents  as  sculpturing  tools. 

Allusion  has  just  been  made  to  the  influence  of 
man  in  modifying  the  scenery  of  the  earth's  surface. 
Perhaps  too  marked  a  contrast  has  been  drawn 
between  the  work  of  man  and  of  other  animals  in 
affecting  the  appearance  of  the  outer  surface  of  the 
globe,  as  indicated  by  the  use  of  the  expression 
"  natural  "  scenery,  and  by  talk  of"  artificial  "  changes 
made  therein ;  some  writers  indeed  speak  of  the 
work  of  man  as  though  it  generally  tended  to  mar 
the  aspect  of  a  country.  When  speaking  enthusias- 
tically to  a  Scotch  boatman  of  the  beautiful  hill 
scenery  of  the  north  end  of  the  Isle  of  Arran,  I  was 
at  first  somewhat  surprised  at  his  remark  that  I 
should  see  the  flatter  south  end  with  its  cornfields ; 
I  was  not  prepared  for  the  influence  of  contrast 
with  the  normal  surroundings,  in  determining  a 
man's  ideas  of  what  is  beautiful.  Anyone  who  had 


CONCLUSION  359 

journeyed  long  in  a  desert  region  would  no  doubt 
be  more  profoundly  affected  by  the  sight  of  the 
cultivated  fields  of  our  own  country,  with  the  rustic 
cottages  nestling  here  and  there  among  their  orchards, 
than  by  the  finest  "  natural "  scenery  in  the  world. 
Nevertheless,  one  would  regret  the  obliteration  of  all 
"  natural "  scenery,  even  if  it  were  replaced  by  a 
harmonious  substitute,  due  to  the  labours  of  man. 
Much  more  does  one  regret  the  mutilation  of  a 
district  rich  in  natural  beauty,  by  works  which  pro- 
duce a  feeling  of  discord — works  which  are  often 
wrought,  not  for  the  general  advantage  of  man,  but 
for  the  sake  of  benefiting  the  pockets  of  greedy 
speculators  to  the  extent  of  a  few  pounds.  And  yet 
this  mutilation  of  some  of  the  fairest  scenes  of  our 
own  country  has  proceeded,  and  is  proceeding,  un- 
noticed save  for  the  words  of  regret  of  a  few  lovers 
of  Nature,  whose  protests  are,  alas !  unheeded  by  the 
great  mass  of  our  countrymen.  America  has  its 
National  Park  set  aside  for  ever,  as  a  thing  of  beauty, 
owing  to  the  far-sighted  intelligence  of  its  legislators. 
We  too  have  our  exquisite  jewels  of  natural  beauty, 
jewels  so  exquisite  that  they  are  prized  not  only  by 
hosts  of  our  own  countrymen,  but  by  others  who 
come  from  afar  to  gaze  at  them.  Devon  and  Corn- 
wall, Wales,  the  Highlands  of  Scotland,  and  perhaps, 
above  all,  the  Lake  District  of  Cumberland  and  West- 
morland, are  glorious  possessions  of  the  English 
people,  where  the  jaded  dweller  in  towns  may  find 
an  exceeding  great  peace.  Do  we  appreciate  these 
as  we  should  ?  Alas  !  the  very  stones  cry  out  against 
us.  The  two  lakes  of  Llanberis,  things  of  beauty  at 
a  time  within  the  recollection  of  the  present  genera- 
tion, are  now  receptacles  of  slate  rubbish,  extracted 


360     SCIENTIFIC   STUDY   OF   SCENERY 

from  the  adjoining  hills,  which  are  marked  by  scars 
that  cannot  be  effaced  till  long  ages  have  rolled  by. 
One  of  the  most  beautiful  upland  hollows  of  Wales, 
which  nestles  under  the  glorious  precipice  of  Snow- 
don,  has  been  sadly  despoiled  for  the  sake  of  a  few 
pounds  of  copper  ore  ;  the  curved  bays  of  Thirlmere 
— effect  of  wave-lapping  along  the  beach  for  many  a 
long  day — are  replaced  by  angular  indentations  of 
the  banks  of  a  reservoir,  made  to  supply  the  thirsty 
folk  of  a  large  town.  This  conversion  of  lake  into 
reservoir  is  justifiable  on  the  ground  of  necessity,  but 
who  can  look  without  indignation  on  the  unsightly 
heaps  of  slate  refuse  which  have  sullied  the  beauty 
of  that  fair  valley  which  was  the  chosen  home  of 
Wordsworth  ? 

The  library  of  Alexandria  was  burnt  down,  and 
men  have  not  ceased  to  bewail  its  loss,  though  the 
chief  thoughts  of  men  which  were  embodied  in  its 
tomes  have  doubtless  been  since  recorded.  The  work 
of  nature  is  being  daily  mutilated,  and  men  look  upon 
the  havoc  with  indifference.  Man  can  here  destroy, 
but  he  cannot  replace.  Ages  ago  the  almost 
structureless  masses  of  jelly  living  in  a  bygone 
ocean,  built  up  an  exquisite  mosaic  of  rock,  formed 
with  almost  inconceivable  slowness.  Other  ages  pass 
away,  and  the  delicate  graving  tools  of  Nature  carve 
out  this  rock  into  spiry  pinnacles  and  impending 
cliffs,  wreathed  with  ivy  and  roses  and  many  another 
plant  Then  comes  man,  and  with  a  few  pounds  of 
gunpowder  destroys  this  work  of  ages  in  a  moment, 
and  the  white  cliffs  of  Derbyshire  are  marked  by 
a  hideous,  indelible  scar. 

Will  this  go  on  always,  and  will  the  English  people 
look  on  with  indifference  while  their  glorious  heritage, 


CONCLUSION  361 

due  to  the  toil  of  Nature's  servants  through  the  count- 
less aeons  of  geological  time,  is  slowly  but  surely 
squandered  ?  Let  us  hope  not ;  let  us  rather  believe 
that  the  time  is  now  at  hand  when  the  national  im- 
portance of  the  question  of  our  natural  scenery  will 
be  fully  appreciated,  and  when  the  study  of  natural 
scenery  will  be  looked  upon  as  one  of  the  most 
beneficial  of  our  means  of  education. 


INDEX 


A. 

Beheaded  rivers,  142. 

Ablation,  289. 

Belloc,  E.,  196. 

Accumulation,  Mountains  of,  55. 
Acid  rocks,  99. 

Bergschrund,  285. 
Blanford,  W.  T.,  145,  244,  262. 

^Egre,  323. 

Blocs  perches,  316. 

Agassiz,  A.,  311. 
Aiguilles,  91. 

Blow-holes,  330. 
Bonney,  T.  G.,  1  86. 

Aitken,  J.,  32. 

Bore,  323. 

Alkali  deserts,  265,  270. 

Boulder-clay,  316-319. 

Alluvial  cones,  137,  142. 

Breakers,  325. 

flats,  132,  196,  233,  235. 
Alpine  type  of  mountains,  62,  63. 
Andrews,  C.  W.,  328. 

Broads,  165. 
Brogger,  W.  C.,  340. 
Browne,  G.  F.,  157. 

Antecedent  drainage,  144. 
Anticline,  14. 

Buckland,  W.,  311. 
Buttes,  247,  256,  258,  259. 

Anti-cyclone,  43. 

Asar,  318. 

C. 

Ashes,  Volcanic,  225. 

Calderas,  217,  218. 

Atmosphere,  29-45. 

Canons,  129,  259. 

Atolls,  344,  346,  347. 
Attributes  of  scenery,  2-7. 

Carses,  348. 
Cascades,  150. 

Avalanches  of  rock,  196. 

Caves,  153-157. 

of  snow,  279. 

in  glaciers,  291,  302. 

Sea,  329,  330. 

• 

Chinese  walls,  298. 

B. 

Cinder-cones,  213,  214. 

Bad  Lands,  256,  269. 

Circumdenudation,  Mountains  of, 

Ball,  J.,  30. 

55- 

Barchanes,  262. 

Cirques,  75. 

Bars,  341. 

Cirrus,  33,  37,  38- 

Basalt,  99. 

Cleavage-planes,  1  8. 

Base-line  (of  erosion),  84,  86. 

Cliffs,  Subaqueous,  190. 

Basic  rocks,  99. 

of  erosion,  193. 

Basin  (of  strata),  14. 

Sea,  327-332. 

Bays,  192,  193,  335. 
Beaches  of  lakes,  188,  194,  265. 

Climate,  Effect  of,  355-358. 
Glints,  108,  246. 

sea,  332-335. 
—  raised,  348. 

Clouds,  31-45- 
Classification  of,  32. 

Beaver-dams,  164. 

Collingwood,  W.  G.,  22. 

363 

364 


INDEX 


Colour,  Effect  of,  4. 

Diversion  of  river-drainage,  140- 

in  the  sky,  29. 

143- 

of  lakes,  198-201. 

Dolomite  mountains,  108,  109. 

of  ice,  308. 

Domes,  Drainage  of,  78. 

Cols,  75-77. 

Volcanic,  211. 

in  meteorology,  43. 

of  strata,  14. 

Columnar  structure,  103. 

Drumlins,  217. 

Combes,  75. 

Dry  deltas,  137,  168,  196. 

Consequent  river-systems,   139, 

Dunes,  260-264,  27°- 

streams,  121. 

Dutton,  C.  E.,  212,  218,  220. 

Continents,  Structure  of,  46-54. 

Dykes,  100. 

Contraction  theory,  47. 
Coral-islands,  344-348. 

Cornish,  V.,  260,  276,  333,  338- 
34I-. 

E. 

Corrasion,  81—84. 
Lateral,  130. 
Crater  lakes,  181,  188. 
Craters,  214-219. 
Crevasses,  286-289. 
Cumulus,  33,  34. 
Currents  of  ocean,  324. 
Gushing,  H.  P.,  162,  185,  300. 
Cuts-off,  165. 

Earth-pillars,  128,  129. 
Earthquakes,  229,  230. 
Ellis,  W.,  222. 
Englacial  rivers,  302. 
Escarpments,  124. 
Eskers,  318. 
Etangs,  164. 
Everett,  Professor,  266. 

Cwms,  75. 

Cyclones,  40-43. 

F. 

D. 

Falaises,  164. 

Fan-structure,  63. 

Dana,  J.  D.,  345. 

Fata  morgana,  202. 

Darwin,  C.,  345,  349. 

Faulted  mountains,  65-69. 

Daubree,  A.,  314. 

Fault-planes,  17. 

Davis,  W.  M.,  97,  121,  124,  139, 

Influence  of,  109. 

142,  145,  147. 

Fens,  239-241. 

Davy,  Sir  H.,  199,  204. 

Firn,  281. 

Dawkins,  W.  B.,  152. 

Fissure-eruptions,  224,  225. 

Deeley,  R.  M.,  282. 

Fjords,  236,  339. 

DelaBeche,  Sir  H.,  115. 

Fletcher,  G.,  282. 

Delabecque,    A.,    158,    163,    170, 

Floating  islands,  198. 

171,    173,   175,   181,   182,    184, 

Floe-ice,  350. 

186,  191,   196,  200. 

Fluvio-glacial  deposits,  294,  307. 

Deltas,  236-238. 

Folded  mountains,  59-65. 

of  lakes,  194-196. 

strata,  14. 

Denudation,  70. 

Foliation-planes,  19. 

Processes  of,  80. 

Forbes,   J.    D.,    167,    281,    284, 

Derivative  rocks,  9. 

285,  295,  297. 

Deserts,  248-271. 

Forel,  F.  A.,  158,  191,  199,  200, 

Desor,  E.,  172. 

202. 

Dewar,  J.,  30. 

Forelands,  338. 

Dip-slope,  124. 

Frost,  89,  90,  92,  272-274. 

Dirt-bands,  295.                                 !    Fuljes,  263. 

INDEX 


365 


Garwood,   E.  J,,   175,  274,  283, 

298,  299,  302. 

Geikie,  Sir  A.,  92,  164,  224,  266 
,  269,  325,  329. 
Gemmellaro,  M.,  120. 
Geysers,  226,  229. 
Giants'  kettles,  3  [5. 
Gilbert,  G.   K.,  60,  69,   71,   122, 

139,    140,   143,   145,    147,    178, 

'??•  '82.  252,  254,  333. 
Gilpm,  W.,  119. 
Glacier-canals,  300. 
Glacieres,  157. 
Glaciers,  279-320. 

Movement  of,  284. 

Remanies,  297. 

Erosion  by,  311-315. 

Glacier-tables,  294. 

Gorges,  118. 

Granite,  99. 

Gregory,  J.   W.,    165,    166,   177, 

283,  298,  299. 
Gulliver,  T.  P.,  338. 
Guthrie,  Professor,  205. 


H. 

Heim,  A,  62,  180. 
IlerschelJ.,  34. 
Hoar-frost,  273. 
Hogbacks,  14,  64. 
Holmes,  W.  H.,  259. 
Hopkins,  W.,  287. 
House-roof  structure,  90,  254. 
Howard,  L.,  32. 
Hummel,  D. ,  318. 
Huxley,  T.  H.,  347. 


Ice,  272-320,  350,  351. 
Icebergs,  307,  308. 
Ice-cap,  298. 

of  Greenland,  303-307. 

Ice-sheet,  298. 
Icicles,  275. 
Igneous  rocks,  9,  98. 
Inclination  of  slopes,  114-117. 
Islands  in  lakes,  197,  198. 


Islands,  Oceanic,  342-348. 

Volcanic,  343,  344. 

Coral,  344,  348. 


J. 

Joint-planes,  16. 

Judd,  J.  W.,  179,  i8r,  205,  208, 

2i',  347- 
Jukes,  J.  B.,  330. 


K. 

Kames,  318. 
Kendall,  P.  F.,  312. 
Kent,  S  ,  345. 
Kettle-holes,  159. 
Kornerup,  A.,  90,  91, 
Kryokonite,  305. 


Laccolite,  60,  100. 
Lagoons,  335,  344. 
Lakes,  158,  202. 

without  outlet,  265. 

Lamination,  Planes  of,  12. 

Landslips,  163,  230/332. 

Lapworth,  C.,  48,  62,  207. 

Lava,  219-221. 

Lewis,  H.  C.,  319. 

Ley,  C.,  33-35,  44. 

Limestone,  Influence  of,  107-109, 

246. 

Livingstone,  D.,  92. 
Llanos,  243. 
Lochs,  Sea,  339. 
Loess,  264. 
Lubbock,  SirJ.,  186. 
Lyell,  SirC.,  118,  120,  128,  132, 

150,  176,  219,  238. 


M. 

Mallet,  R.,  205. 

Massive  eruptions,  224,  225. 

Master-joints,  1 6. 

McMahon,  A.  H.,  263,  264,  266. 

Medanos,  262. 


366 


INDEX 


Medlicott,  H.,  145,  244. 

Parasitic  cones,  219. 

Meres,  159,  174,  186. 

Passes,  75-77- 

Mesas,  247. 

Peat-mosses,  171,  197,  235. 

Metamorphic  rocks,  10. 

Penck,  A.,  173. 

Mill,  H.  R.,  158,  184,  189,  193, 

Peneplains,  97,  247. 

194,  197. 

Perched  blocks,  316. 

Miller,  S.  H.,  239. 

Piedmont  glaciers,  298,  300,  301. 

Milne,  J.,  96,  213. 

Plains,  231-243,  319,  342. 

Mirage,  202,  266. 

Planation,  145. 

Moels,  87. 

Planes  of  lamination,  12. 

Monadnocks,  147. 

Planes  of  stratification,  12. 

Monoclinal  faults,  66. 

Plateaux,  231,  243-247. 

Monocline,  14. 

Polders,  243. 

Moraine  lakes,  159. 

Ponding,  143,  176. 

Moraines,  292-295,  306,  315,  316. 

Potholes,  118,  153. 

Mortillet,  G.  de,  183. 

Powell,  J.  W.,  67,  145,  244. 

Moulins,  290,  303. 

Prairies,  243. 

Mountain-range,  62. 

Puffing-holes,  330. 

Mountains,  55-112. 

Puys,  219. 

of  deserts,  254. 

Pyramidal  hills,  no. 

Movements,  Effect  of,  7. 

Mud-volcanoes,  229. 

Murray,  SirJ.,  345. 

Q. 

Quartz-veins,  109. 

N. 

Nansen,  F.,  303. 
Needles,  332.             . 
Neulinge,  260. 

R. 
Race,  323. 
Ramsay,  Sir  A.  C.,  115,  176,  183, 

Neve,  281. 

3!3- 

Nimbus,  33. 
Nordenskjold,  Baron  A.  E.,  300. 
Nunataks,  305,  306. 

Reclus,  E.,  236. 
Reefs,  Coral,  344-348. 
Reid,  C.,  153. 
Richthofen,  Baron  von,  210,  264. 

Rivers,  erosion  of,  80,  232. 

O. 

Deposits,  232. 

Oases,  270. 

River-terraces,  234. 

Obsequent  streams,  124. 
Oceans,  46-54,  321-351. 
Oldham,  R.  D.,  180,  185. 
Osier,  A.  F.,  33,  36. 

Roches  moutonnees.  312,  313. 
Rock-basins,  181-187. 
Rock-structure,  n. 
Influence  of,  on  denudation, 

Otley,  J.,  198. 
Outcrop,  13. 
Overfault,  66. 

97- 
Rock-texture,  II. 
Roflas,  172,  314. 

Overfold,  66. 

Ruskin,  J.,  3,  4,  6,  19. 
Russell,  I.  C.,  178,  300. 

P. 

S. 

Pack-ice,  350. 

Pampas,  243. 
Parallel  roads  of  Glen  Roy,  162. 

Sand-banks,  334,  340,  341. 
Sand-dunes,  260-264,  27°. 

INDEX 


367 


Sand-pillars,  266. 

Sand-storms,  266. 

Sandstone  hills,  105-107. 

Savannahs,  243. 

Schist-hills,  104,  105. 

Scott,  R.  H.,  33,  34,  45,  274,  276. 

Screes,  90,  96,  168,  196. 

Scrope,  G.  P.,  182,  204,  211,  212. 

S-curve  (of  rivers),  131. 

Selvas,  243. 

Septum  (of  fold),  48,  49. 

Shales,  Influence  of,  107,  134. 

Sheets  (of  igneous  rock),  100. 

Shores,  of  lakes,  188,  191-197. 

Sigmoidal  folds,  66. 

Sills,  100. 

Sinter-terraces,  228,  229. 

Size,  effect  of,  3. 

Skertchly,  S.  B.  J.,  239. 

Slate-hills,  105. 

Smith,  E.  A.,  177. 

Snow,  275-279. 

Cornices  of,  276. 

Red,  309. 

Snowflakes,  273. 
Snow-line,  277. 
Sollas,  W.  J.,319. 
Spencer,  J.  W.,  179,  190. 
Spring,  Professor,  200,  201. 
Springs,  73. 

Hot,  226-229. 

Stacks,  332. 

Stalactites,  155. 

Stalagmite,  155. 

Steenstrup,  K.  J.  V.,  288. 

Steppes,  264. 

Strahan,  A.,  119. 

Stratification-planes,  12. 

Stratified  rocks,  10. 

Stratus,  33,  35-37. 

Striation  (glacial),  311,  312,  351. 

Subsequent  streams,  121. 

Superinduced  drainage,  144. 

Swallow-holes,  153,  154,  173. 

Symmetrical  mountains,  64. 

Syncline,  14. 

T. 

Tarai,  243. 
Tarns,  166. 
Terraced  hills,  103. 


Terraces,  River,  234. 

Texture,  Effect  of,  7. 

Thalweg,  126. 

Thunderstorms,  44. 
I    Thrust-faults,  66. 

Till,  316. 

Tors,  103. 
I    Transportation,  81. 

Tundras,  243. 

Turbary,  197,  235. 

Tyndall.J.,  24,  34,287. 


U. 

Uinta  type,  64. 
Unconformity,  51. 
Underground  rivers,  152-157. 
Unsymmetrical  mountains,  64. 
Upheaval,  Mountains  of,  55,  58- 
69. 

V. 

Valleys,  113-157. 

Classification  of,  113. 

Vallot,  J. ,  196. 

Vegetation    on    mountains,    in, 
112. 

in  lakes,  197,  235. 

on  deltas,  238. 

of  fens,  240,  241. 

in  arctic  regions,  243. 

of  deserts,  267-270. 

on  glaciers,  302,  304,  309. 

on  nunataks,  306. 

alpine,  319. 

marine,  349,  350. 

Verglas,  274. 
Volcanoes,  203-230. 

Mud,  229. 

V-shaped  depression,  43. 
Vulcanicity,  Causes  of,  203-210. 


W. 

Wadys,  259. 
Wallace,  A.  R.,  356. 
Waltershausen,  S.  von,  218. 
Walther,  J.,  253-258,  260. 
Ward,  J.  C.,  102,  184,  316. 
Warming,  E.,  270. 


368 


INDEX 


Warping,  175. 
Waterfalls,  147-152. 
Watersheds,  52,  54,  71-80. 
Watts,  W.  W.,  169. 
Waves,  321. 

Erosion  by,  324-332,  337. 

Weathering,  81. 
Weed,  W.  H.,  228. 
Whirlpools,  323. 
Whymper,  E.,  114,  208,  209. 


Wilkes,  Lieutenant,  218. 
Wind,  Action  of,  93,  182,  219. 
Wordsworth,  W.,  3,  5,  6. 


Xerophilous  plants,  268. 


Zeugen,  256,  257. 


PLYMOUTH 

ILL1AM   BRENDON    AND  SON 
PRINTERS 


